I have a C5 up & running with about 30 ZWave+ devices and 6 Zwave devices. I also have a C7 hub waiting for all of the issues to be ironed out.
When the time comes to move my Zwave devices to the C7, are there any benefits/issues with leaving my Zwave devices on the C5 and moving my Zwave+ devices to the C7 and then slowly replace my Zwave devices? My assumption is that the Zwave mesh is only as fast as it's slowest link so if I keep all of my Zwave devices on C5 and move all of the Zwave+ to C7, then my Zwave mesh on C7 will be faster overall than if I move all of my Zwave devices to C7. Is assumption true or am I overthinking?
Assuming you have a strong enough mesh (enough repeaters in the right locations on both), there's nothing wrong with doing this. However, you might be overthinking: it's true that you'll be limited to the lowest speed in the route but that's not necessarily the lowest speed on your network. If your device doesn't hop through that device, it doesn't matter. This, then, also only matters for repeaters. I sort of did what you're thinking now a while back, minus keeping two networks: I replaced all my repeaters with Z-Wave Plus (500-series) devices to eliminate "classic" Z-Wave repeaters on my network. I still have a few "classic" Z-Wave sensors and whatnot, but I don't care enough about those to replace them until they finally break or something better comes along. Maybe some day I'll do the same with 700- vs 500-series repeaters, as the C-7 is 700-series, but I don't think that's quite as near of a benefit, to say nothing of how hard 700-series devices are to find in most markets right now.
You're dealing more with Potential than anything else. There are 3 communications speeds possible for ZWave... 100K, 40k and 9.6k.
All devices must support 9.6k therefore, as distance increases, signal noise increases and the devices reduce communications speed to compensate. Putting all your + devices on a single mesh is probably a good idea, BUT don't expect all conversations at 100k. You may still have spots in your home where communications are reduced. Obviously more repeaters become the solution.
I just thought of something else that might matter: if you have vintage GE or similar switches that don't report instant status from physical events back to the hub and you care about that (enough that you have Z-Wave Poller installed right now), then I could see a potential benefit to keeping those puppies separate. Some people have reported poor Z-Wave performance with polling, though likely only if they poll "too much" or have a weak network to start with. If you do this on its own hub, you could risk knocking yourself out with polling and at least everything else would work fine.
I do poll my Zwave switches but from NR, not the hub, and only every 5 minutes. Also, as I have added Zwave+ devices, I have swapped them with existing Zwave devices and moved the existing Zwave devices to where I don't necessarily need to know their status every second of every day. Additionally, my 6 Zwave devices are all located on what I would call the outer limits of my mesh so it would be less likely that any Zwave+ device would choose to go thru a Zwave device. For example, 3 of my Zwave devices are for exterior lights that I don't use physically; they are set to turn on/off based on motion or sunrise/sunset. The other 3 are in a mostly unused guest bedroom that is the farthest away from my C5 hub.
And yes, all of my Zwave switches are GE but I don't know they qualify as "Vintage".
Lots of good advice already here. But if its only 6 zwave devices, I would just go and replace them all one time and save the headache, or at a minimum, replace the devices that repeat so they don't slow down things if they get put into a route.
I did that and got rid of all my zwave devices (except for a couple sensors) and swapped them all over to zwave+ and it made life a lot nicer in terms of speed and reliability.
