Noel Borthwick [Cakewalk]
I used CCleaner for the cleanup to remove all the dead stuff from old programs etc. Nothing manual.

Cheers.  Good tip!

Brandon Ryan [Roland]
My take is that, while SONAR X2a runs great on Win7, it arguably runs even better on Win8 and I prefer Win8 in general (startup time, copy process, apps when needed, etc).
 
As others have said though it goes beyond SONAR. You'll need to make sure your other devices are happy with Win8 also, which is likely, but good to double-check.

As I've stated ad nauseum,  X2a doesn't work well on my Win 7 system.  Those of us who have been having problems with buggy take lanes seem to be using Win 7.  I also notice longer load-times and more drop-outs.  I have hypothesized that whatever Cake did to optimize it for Win 8 has screwed up compatibility with Win 7.  Definitely go with Win 8.  I can't keep buying a new computer every two or three years, so I'm back to X1.

One thing I'd say to the OP that no one seems to have mentioned is that the difference between XP and windows 7 in terms of familiarity and learning curve is quite small to that between XP and windows 8.
 
Windows 8 is very different and there have been a lot of complaints at the way microsoft have seemingly abandoned desktop users and are more interested in touch screen and apps and tablet users. No longer is there a start button and no longer do you go straight to your desktop. The good news is that microsoft are apparently working on an updated version where you can have the start button and desktop as they were.
 
As for better performance windows 8 is proving to be better but only by a very small margin as suggested here bench mark tests. This is the only benchmark test I've seen to date and others will probably give slightly different results depending on what software is being used.
 
Did I read that you could download a 30 day demo of windows 8.1 or did I dream that ?
If so then you might want to try it (if you have the time and patience) as you might not like the changes and wish you'd gone with windows 7. If you have, or will soon be investing i a touch screen monitor then that would be a better reason to go with windows 8 right now as X2 is being designed to utilise touch screen technology.
 
Steve

twaddle
One thing I'd say to the OP that no one seems to have mentioned is that the difference between XP and windows 7 in terms of familiarity and learning curve is quite small to that between XP and windows 8.
 
Windows 8 is very different and there have been a lot of complaints at the way microsoft have seemingly abandoned desktop users and are more interested in touch screen and apps and tablet users. No longer is there a start button and no longer do you go straight to your desktop. The good news is that microsoft are apparently working on an updated version where you can have the start button and desktop as they were.

There's already an excellent free program call Classic Shell that gives you back the Start Button and boots to the desktop; and by the sounds of it, it's also much better than MS's 8.1 "fix".