@ steve
i think it depends on the hardware when you compare xp/vista.
on new hardware with fast cpu/graphics the differance is probebly small,
but on older/slower hardware the differance will be big.
i have look at your link to tomshardware and the test setup is verry high end so thats not a real worlds test, a average user wil never use this system, a real test would be with budget system or a system thats about 1-2 years old.
Biting the hand that feeds IT
