XP still runs fine for me and the only sims I have installed are FS9 and CFS2. As long as this old comp will hang in there, I'll stay where I'm at.
I'm kind of in the same boat. Current rig runs fine but I want a new PC to run FSX that I've had for 2 or 3 yrs but never been able to enjoy, but by the time I get a new PC the next version of MSFS will come out and whatever rig I get probably won't be able to run it so I'll end up in the same spot.