You really have no clue about this stuff do you? First it was the mics and drum question which seems like basic knowledge someone looking to do this for a living should know, now it's whether you should back up your files before making an Operating System change.
Ask your self this simple question since you are supposedly in the middle of recording several bands - will they be happy if during your upgrade it fails and you can't get back to work in a matter of a few hours or a day at the most?
Seems you ask questions that just make some people go huh! Really? Huh!
I don't record bands at all - I just record my own stuff as a solo musician and it would piss me off if I could not get my complete system as it was in a matter of a day and I only answer to myself.
Do yourself a favor and get a good backup plan in place prior to doing any significant change to your system.
By the way - Windows 7 is a super stable platform for recording - I use Sonar PE x64 on my Windows 7 x64 build and it's rock solid, however like most things in life - your mileage may vary.