In my case, I have both 8.0 and 8.1 on thumbdrives - however, I'm shaking down an AIO based on the WZOR leaks (sorry, x32 fans - this AIO is x64) to replace the standard x64 8.1 on my thumbdrive.
The reason for this AIO:
1. It works for clean installs and upgrades, and from any SKU of 8 out there.
2. It's no bigger than the standard ISO.
3. Unlike the standard ISO, it can upgrade 8 ProWMC installs.
I'm trying to shake down one rather odd bug (in one game, DC Universe Online) - in the game, the F1 key on my keyboard doesn't work if I install the game first in 8.0, then upgrade to 8.1; however, it works fine if I install in 8.1 directly.