You want "full fps" (60 fps). That isn't going to happen cuz of rendering options.
Frame Rate Rules
Below 19 is terrible
25-35+ is great
60+ unlikely but possible in the future
You can't fully max out XP on any pc on today's time. You want to play with oculus rift VR BUT it is impossible for now to run that with XP. Oculus Rift requires at 75 FPS or more to function. Last time I checked, you can't get 75 FPS on XP unless you tone down the graphics to the lowest possible setting.
When VR becomes available for flight sim in a couple yrs of more, I am willing to pay $600 for a great VR headset
Right now, it simply isn't possible to run XP with decent eye candy and get 75 or more FPS
As for your pc, processor must be over 3 ghz, graphics card must have 4 gab VRAM, must have 8-32 gb RAM and decent cooling + a high quality PSU
-Rishi