A 2GHz quad core is more useful for current games than a 3.2 GHz dual core - from what I could bench on my oldie Athlon II X4, at least, which gives me some leeway when it comes to core configuration and clock speed in BIOS. Hyperthreading may help a lot when it comes to resolving that difference (thus why an i3 can be seen as a minimum for gaming for some), but a quad core is pretty much required nowadays.
Note that I also have an i5@4.2GHz, with higher IPC and clock than the AMD X4, but while the i5 is a definite improvement over the AMD X4, I see less difference between them as quad cores than between the X4@2.0GHz and it as an X2@3.2GHz.