Radeon HD 7750 vs Geforce GT 640

Not sure how much you can rely on hwcompare, you better off reading reviews about both cards but i would guess the 7750 to be faster.

According to that site my old video card is faster than my current one, but that is not the case. the architecture of the 7750 and the 640 are very different to compare them by only looking at their raw power, you have to look at the final result with benchmakrs.