Ok so I noticed something a bit weird:
I never used the z-wave stick that came with the c5 because I was continuing to use the c4 for most stuff and c5 for additional processor intensive stuff.
Now that I am switching them around I took a look at the stick that came with the c5... and its a uzb7 - i.e. 700 series - so... does this mean if I copy across my z-wave backup to this using a computer I could just use that with the c7 snd get all the additional benefits straight away?
I am not experienced enough to give you some good advice for that. I think technically you could backup the Z-Wave table via some other sw (PC Controller maybe?) and restore to another one but don't know if you could with different models. Maybe someone else can chime in with this.
On a side note - UZB-7 came with a C-5? That's very cool thing although not a US configuration as we use the internal radios. We have to buy ours separately if we want one. Good news is the price is not bad at $20 USD.
Currently I don't believe the C7 will look at any external USB radios at all so I don't think that would work.
From what I've gleaned the ZigBee chip across C7, C5 and C4 (external Nortek) is the same, so technically I don't believe there's any reason why the Nortek wouldn't work in the C7 for ZigBee like it does in the C5. Obviously I don't know how Hubitat works internally but from a purely Linux OS point of view I would imagine it's just a case of pointing their software at the right port that's created when the stick is plugged in.
What stick are you currently using in the C4 for Z-Wave?
I still think that if you have a C5 to hand, the thing to test would be using an OTG USB hub such as https://www.amazon.co.uk/AuviPal-Adapter-Playstation-Classic-Raspberry-Black/dp/B083WML1XB and then plug in both the Nortek and separate Z-Wave stick.
I don't see any reason why that wouldn't physically work, as in the USB hub would be recognised and present both sticks at the OS level. It's just what the Hubitat software would do at the software level.
From other reports we know that the C5 will pick the Nortek for both ZigBee and Z-Wave over the internal radios, but I don't think anybody has ever tried to see what it would choose if presented with a third option i.e. a separate stick for Z-Wave.
Perhaps we don't need another data point but I converted my oldest C-3 to a C-5 a few minutes ago. It could not have gone smoother.
This particular Hub is ZWave only. Zigbee has always been disabled. I have had 3 development hubs for years and maybe 6 weeks ago I shut one down and "factory reset" it, put it back in it's original box, threw it on a shelf. Today, I powered it up and restored the C-3's backup. I had to re-register the C-5, but that took less than 30 seconds.
Then I powered down the C-3 and put the ZWave stick in the OTG of the C-5 and spent the next 15 mins hunting for a microUSB power supply, before remembering there was one in the original box under the cardboard (forehead slap) 
[I've been using POE for all my development hubs and thus it had been years since I looked at its PS. There's no POE in the room where the C-3 lived.]
In another topic, the C-3 and a C-4 I have, were showing high temps relative to the C-5's and C-7's. I had stuck a small fan an inch or two from the C-3 and it's temp dropped from 60-70C to 48C. Now the C-5 that replaced the C-3 has no fan aimed directly but is running at 31C, in line with the C-7's.
During the C7 hardware beta I asked the question on whether adding a usb stick radio would work and was told by staff that it would not, as with the 700 chip additional sticks for different countries was not needed
Andy
That's interesting .... so it will recognise an external (separate) Z-Wave stick correctly. And we know it recognises the Nortek stick as both ZigBee / Z-Wave.
I think @AdamV wants to know if (via an OTG USB hub) it will correctly use ZigBee off the Nortek stick and Z-Wave off a separate stick (rather than use Z-Wave off the Nortek stick).
Yeah that makes sense.
For ZigBee though the hope still stands .... that it might one day be possible to move the Nortek from an older hub to a C7, restore a backup and be back in business.
Yea, it's a good puzzle. 
There would be 3 ZWave radios and two Zigbee. I think we already know that the platform picks an external over an internal, thus the external Zigbee would get the nod. But what about when there are two external ZWave? It will pick one, I'm sure of that, but which one and will it always pick that same one across reboots becomes the real puzzle for me.
There are C-5's shipped with the Nortek (ZWave & Zigbee) and C-5's shipped with just a ZWave stick (eg: zwave.me). Equally there are C-4s that were shipped with a Nortek for Zigbee and that regional ZWave stick (eg: zwave.me) and THAT is the case that suggests the platform will chose the "Not-Nortek" Zwave if it's available. Internal then External Nortek then External (other) is the implied detection order... and it sticks with the last found.
I tried this recently (just to test) and it didn't work for me. I can't rule out a bad OTG cable or even a bad stick , so I wouldn't take this as a definitive result, but my assumption is still tht it doesn't work.
Luckily, Zigbee is pretty easy to re-pair, even if it's not fun, so this doesn't concern me nearly as much as the work or redoing the same with Z-Wave would!
Emboldened by my success with my C-3 I decided that today was an auspicious day to also move my (production) C-4 to a C-5. I have been using the C-5 as my only development hub and so I had to discard that use for now...
I did a Soft Reset on the C-5 and restored the C-4's backup. This particular C-4 has both Z-Wave and Zigbee via the Nortek stick. I then powered down both hubs and moved the stick. I use static DHCP so I had to adjust that, then powered up the C-5. And that was it.. both ZWave and Zigbee came back. (Zigbee took a couple minutes to stabilize (red dot in the upper right corner) but after that wait, it's all good.
Now my 4 Production hubs are: two C-5's and two C-7's. The C-3 is permanently shut. A C-4 is permanently shut and the other C-4 is now my development hub, having the backup from the C-5 restored on to it.
That's what I was thinking ..... I have C4's with Nortek and external Z-Wave .... I don't use the external Z-Wave though as I use C7's for Z-Wave stuff. So the C4's are ZigBee only.
I really want to move from C4 for reasons already discussed many times, so currently waiting out in hope that a move to the C7 with the Nortek (for ZigBee) might work in the future. If not then I will probably follow others and try and track down some C5's.
Oh it definitely doesn't work on a C7 as I've tried it a few times now on my dev hubs, my guess is that the platform when running on the C7 is hard coded to look at the onboard chips only for both Z-Wave and ZigBee. So it would need Hubitat to put something in place like it seems they did for the C5, so it uses the external stick if it's there.
A lot of the C-7's "advantage" is all the tools for understanding the mesh. I'm not saying they couldn't be back ported, but it is not at all like including both ZWave SDKs. Half of the UI wouldn't work and thus there'd be Topics about that... 
Seems like that would be worse, in my opinion.
Oh yeah for sure it likely would be too much effort for Z-Wave but for ZigBee I would imagine it's only a port change. Pure speculation on my part of course!
I think the maths is a bit different for me because I'm in the UK. So the C4 came with a separate zigbee and z-wave usb stick, each one only does the one radio, its not a dual radio nortek stick like you have in the US - in fact I don't even think it's Nortek at all.
The C5 has the internal radios (i cant remember if it has both z-wave and zigbee internal... but it definitely has zigbee) nonetheless it came with the external uzb7 - again I don't think it's Nortek, and I'm pretty sure it's z-wave only..
So... in an absolutely ideal situation this is what I would like to do... I'm not sure how much is actually possible:
Seems like the multi port OTG is worth a try...
Plug both external sticks into that and see what you get. Then report back to us, of course 
Did this swap over a month ago and not looking back. C5 has fixed all my issues I had with a C4. Hubitat needs a buy-back program.
I wasn't having any trouble with my C-3 and C-4's. I made the swap mostly because I could and wondered if it would make a difference. I can't say that it has, but it's only been 10-12 hours
In other words, I knew I could swap for a long time but didn't because Murphy's Law is always nearby. I've swapped my Development systems a dozen times at least but touching Production is still: "do I have time to recover?"
I've decided before I attempt any of this stuff I should make a copy of the original stick - so I've ordered the exact same UZB3 that the C4 came with... may take a while to deliver - so I'll update this thread when its delivered and. been attempted
I was having stability issues with my C4 a year ago. Frequent freeze ups and need to reboot at least weekly. When we moved, since I was going to have to replace everything any way I took the opportunity to introduce a C7. I think out of concern for the freeze up and rebooting issues, i have the apps, and rules , etc. on the C4, but the actual devices and limited apps on the C7, using hub mesh. I started by using Hub Connect, but a few months ago I changed out the router and that completely messed up everything (it shouldn't have, but it did) , and I could never get hub connect to work again. I ended up removing it, switching to hub mesh and ultimately wound up rebuilding the entire mesh again. Thank goodness it was small and didn't take much time. Honestly I spent more time updating firmware and trouble shouting one device that wasn't playing well with others. Now that i have that all settled down, its purring like a kitten. and I am about to move into the next phase of expanding my home automations.
I can concur that C4-->C5 is a good jump! nothing life changing but its slightly snappier - especially when using the web interface.
@csteele The usb hub does work but the C5 will only recognise the external Z-wave stick, not the Zigbee stick... so you are forced to repair all of your zigbee devices. Luckily for me this was doable as I have 24 and they are all in accessible or not too hard to access places... however for Z-wave... I absolutely cannot afford to re-pair them as I have over 100 and some would require a builder to come over to get access to them
I've still got the new UZB3 on order.. and hopefully when it comes I can make a working backup of my current UZB3 and then use that for any experimentations to get it on to the UZB7
I’d be interested if you can pull this off for me to have a migration route. Please document if you do it.
Download the Hubitat app
