How to? Separate OS/APPs and Users to separate drives?

[dnanian]

Well, I guess my answer is "I wouldn't do that". Instead, how about trying a Safety Clone/Sandbox, created on the fast drive?

Putting your User folder on a different drive is a configuration that's not widely seen, and can cause compatibility problems with certain applications. But a Safety Clone is more of a "temporary" setup like this. You'll basically create the Sandbox on the fast drive, and it'll contain the OS and some applications. You'll boot from it and that'll give you the speed, but your user files will remain on the original drive.

It's kind of the best of both worlds. You'll continue to back up the regular drive, because that's where your files "really" are.

Does that make sense? I think you'll find it a lot easier, and more maintainable!