Question about 32bit VS 64bit

[tweaker3]

I play a online simulator called Iracing and have tried it on both XP32 and Vista64 (dual boot) and the 64 allows me to max out all the settings ( 16X Anisotropic, 4X Anti aliasing, Trilined, Vertex. Shadow...etc.) and runs at a smooth 60FPS, but when in XP32 with all the settings maxed it will only run at 25-30FPS.
Is this because of the 64bit bus or what?

Thanx

My system;
Amd 7750 overclocked to 3.2
XFX 4870 1 GB GDD5
4 GIGs OCZ Reaper 1066 DDR2
ASUS M3A78-T Mobo

 

[computabug]

64bit has more bandwidth I believe. I think it's theoretically twice the bandwidth of 32bit? Correct me if I'm wrong lol.