Over at the [H] they have their Real World Gameplay CPU Scaling
review. It puts the Intel Core i7 920 up against the Intel Core 2 QX9650, AMD Phenom II X4 810 & AMD Phenom II X3 720 BE.
But you PC is not just used for gaming, you should also look at benchmarks for apps also. My advice if you can afford it go with a i7 920, if not the AMD Phenom II X4 810 would suite you well.