Sorry, but where is the track file in there?
There are a lot of files but no *.trk.
I would like to compare your track. To me it seems like your Windows XP is to slow. You oced your 8400 to 3,9 GHz. I have my 8600 clocked @ 4,2 GHz and I have average FPS with the original stress test track around 80 - 90 with 1680x1050 and the same settings as yours. I dont think that my 280GTX is the only reason that doubles the FPS. And my AF/AA settings are actually at 16/4 (you used 8/2).
As far as I know BS could only use 1 core (correct me if I am wrong). So the best that can happen is that other cores using the all other programms that are running in the background. I dont know how that could result in doubling the FPS with Windows 7.