More GHz means absolutely nothing. It is the CPU architecture that matters. Just think about it, a pentium 4 at 3GHz got released 10 years ago - and most CPUs have not moved far away from that frequency anyway. Still, any modern CPU at 3GHz, even if you disable all it's other cores and leave a single one, wipes the floor with old pentium. It does much more work per single cycle.
Intel's CPUs are better for gaming than AMD's for the simple reason - they have better single thread performance (performance per core). And core i5 is the best there is for gaming at the moment. There are faster CPUs out there, but having more than 4 cores is useless in most games - they simply prefer fast cores to their sheer number.
I'm not saying that AMD is a bad solution - it will work and it will do the job just fine. Heck, for rendering tasks FX8xxx can even be better. But if you need gaming performance, go fir intel.