Been researching and looking into this.
I had some terrible experiences with the c5, and my research is saying the c8 pro is stable and automations run fast and it easily supports over 100 devices.
How has everybody else’s experience been with the c8 pro over the c5?
Both have run great for me. I have phased my C-5’s out of production and only use them for testing now. Love the new features available on the C-8 Pro.
I never had a C5 but I am currently running a C8 Pro and have had zero issues. I couldn't be happier. I have well over a 100 different automations. Mostly from Rule Machine. I run the Homekit Controller Application that is only available on the C8 Pro. I run Unifi Protect Application and a host of others. I have a mixture of Zigbee, Z-wave, and Matter devices along with some devices coming over from Home Assistant totalling 264 devices. The hub is fast, responsive, and never misses a beat.
I have a C-5 and a C-8 Pro. Truth be told, the C-5 does ALL the heavy lifting. I got the C-8 Pro to replace the C-5, originally. However, today the C-8 Pro just hosts the devices (Zigbee, Zwave, and Matter) and shares them to the C-5 via Hub Mesh, where ALL the automations and complicated logic runs entirely on the C-5.
I bought the C-8 Pro as a replacement for the C-5, but in the end I still use both and oddly enough the C-5 still does all the hard work. The C-8 Pro essentially just acts as a data broker while all the data processing happens on the C-5.
Note that the C-8 Pro is unable to work with some of the older Zigbee devices because of the newer Zigbee chip on the C-8 Pro. The solution is to put such devices on the C-5 and Hub Mesh them over to the C-8 Pro.
Is that stated anywhere on official documentation? My experience has been great with all my older zigbee devices on my C-8 Pro.
Correct.
Yes. Read the section on Iris V1 (AlertMe) devices in the link below. These devices can only be paired to the C-7 and earlier models.
In a way. They key is for the device to fully comply with the Zigbee protocal. Unfortunately some device manufacturers didn't fallow the spec fully to try to create vendor lock in. If reverse engineered it seems hubitat was able to provide support for many of those occasions. The C8 and C8 Pro's new zigbee 3.0 radio is less tolerant of devices not following the spec properly and the work arounds for support didn't seem to work.
As far as what the OP is asking the hard ware changes have been mostly with radio the same processor was used all the up to the C8 Pro. It got the next gen of that processor. Think like going from a intel 12th gen to 14th gen CPU. Allong with the new gen CPU several other things came with it by default. It also got a memory capacity bump to 2GB of RAM. That said i was running over 100 devices on a C8 with the smaller amount of memory. Each environment and use case is different and so though a C8 Pro will certainly have a better chance at meeting thr OP's expectations I would be cautiously optimistic. No matter how you look at it all of the hubs run on a low power ARM CPU SOC designed for ultra low power first. These are easily overwelmed given bad pratices. They are very capeable if you use good pratices though.
So what’s your recommendation then?
Well there is no doubt tbe C8 pro is an improvement over the previous hubs in almost everyway. The faster processor/SoC that brings many other improvements with it as well as the increased ram will have significant overall benefits.
So ofcourse if you have any questions about the robustness of the platform that is the way to go.
Then review your appa and rules on the previous hub to implement best practices as much as possible. Those would be to try to minimize jobs that repeat on short timers for tasks/jobs that trigger on events. Minimize the use of polling as much as possible. Be careful with Lan Integrations as they can be heavy handed with their usage of the hub CPU.
Lastly remember that each of us use our hubs somewhat differently so each of our experiences are different. The key is to find how it worka in your use case.
Also don't forget this community is here to help. If you start to have some kind of issue folks here will certainly try to help you figure it out.
Thanks.
My main complaint with the c5 was motion lighting not being consistent or not fast enough to turn a light on with motion compared to other platforms.
Per ChatGPT, the c8 pro fixes all this?
I would be careful about trusting ChatGPT with subjective answers like that. The key is it could be, but there are many factors that play into it some of which it may not be able to predict or can fluctuate.
First I would ask first for clarity on what you man by fast enough, or consistent. Are we talking half a second, or several seconds? When you reference consistency are we talking about the time is takes to activateare just ranging, or are we talking about it not firing at all?
I can think of a few ways thoughs things couold have nothing to do with the hub itself.
I would also ask for what devices are involved. Are they Cloud based, use Local LAN API's, Zigbee, or Zwave. If they are Zigbee or Zwave what is their version of those technologies they are using.
Sorry if it seems i am making it more complicated,
All very good questions.
Have you configured your Radio RA2 Main Repeater to use a different Lutron Clear Connect channel from the Caseta SmartBridge Pro?
If they use the same exact Clear Connect config, there will be a slight delay. This has been observed when Pico remote is used to trigger a Hubitat automation that in turn sends a command to a Lutron switch/dimmer. Even if two Caseta SmartBridge Pros are used, this delay was observed. However, using a Radio RA2 Main repeater for the Pico remotes, on a different Clear Connect channel, resolves the issue.
Is this how your Caseta and Radio RA2 are configured?
See this post for more details. Your Radio RA2 motion sensors are essentially the same as Pico remotes in how they are used to trigger a Hubitat automation. Thus, they are susceptible to the same delays.
Yes, I'm pretty certain I did this years back. I'm currently using another HA system and remember running into something like this back then.
This beggs the question are we certain the delay is in Hubitat and not the other hubs somehow? Have the live logs on the hub been reviewed to show these deleys are in the Hubitat hub?
Great! I personally have gone from an original C3 hub, to a C5, to a C7 + C8, to a single C8 Pro hub. The C8 Pro allowed me to consolidate back down to a single hub (instead of my two hub config). The C8 Pro hub is definitely quicker than the older hubs. Even just performing a Hubitat platform update, is significantly quicker than the older hubs. Whether or not it will improve your motion lighting automations??? 
I know it definitely won’t make them slower.
During this time of troubleshooting back when the c5 came out, it was narrowed down to the hub. Same devices on a different HA platform at the time proved to be related to the raw horse power of the c5.
I went as far as creating my own custom groovy code to prove the the normal motion sensor time was around 500-750 ms in comparison to 150ms on a different system.
This. It’s pretty hard to answer OP’s question without knowing why he was running into issues with lighting automation reliability while using a C5 hub.
The C8 Pro is undoubtedly faster/more powerful and the platform has matured in several ways over the last few years. Will that result in an improved experience for this user and their previously stated complaints? Hopefully, but who knows?
FWIW, I’m pretty sure older posts by OP are under the username @mik3. Please correct me if I’m wrong.
Correct... I aimed to distance myself from the surrounding drama during that period in order to concentrate fully on the fresh opportunity at hand.