I can understand the apprehension to upgrade as opposed to a fresh clean install. I have three computers one was an XP system and the other two were running Vista one of those was my DAW,two of them are 64 bit. I picked up a three license install disk from Microsoft for a really good price Win7 home 64 or 32 bit option. The upgrade installations of all three went off without a problem. I am convinced that if you have no issues with your present OS then an upgrade isn't a problem.
I feel I saved a lot of headaches by not opting to reload all of my drivers and software again. If I were starting from scratch then a fresh install would have been my first choice,but for those of us with a lot of software relocating all of those serial numbers and codes /re organizing file locations can be a real pain .
If you are using Vista it's your call but with the approach of win 8 Win 7 might come down in price and Win 8 for 69.00 is very reasonable IMO.
I am not adding anything touch screen to my machine in the near future nor am I adding "apps" which seem to be one of the points of focus in Win8. Win 7 should play well with X2 for a long time to come.
I ran Sonar in Vista successfully for a long time and it seems that it will play ok with vista now but if it were me I would have no desire to keep with a program that 1. Is no longer going to be supported and 2. was probably one of the biggest bungles by Microsoft in a long time in terms of reported user problems. Personally it worked ok for me but with a rewritten X2 who knows how it will behave?
I wouldn't want to be sitting at the end of a three week track session and have a problem that blows it all away.
I'm sure there are some horror stories of upgrading, maybe I was fortunate but I think even a side install would get you there and reasonably.Keep both OS if it makes you queasy to upgrade.JMO