FWIW - when Windows 7 came out, I had a Vista system that ran great for my DAW. I liked the improvements in W7 for my office machine so I decided to try it on my DAW. I imaged the drive so I could change back and installed W7 on top of VIsta (something I would never would have done, except it was only a test). I was just going to see what complications there might be if and when I upgraded to W7 and fully intended on reverting back to Vista.
Well, it worked out so flawlessly that I still haven’t reinstalled clean. It is the only computer in literally hundreds I’ve used that I did an upgrade rather than clean install and have yet to experience any problem whatsoever.