Personally, I'd be building a rig on the P55 chipset. X58, and Hxx are not cost-effective right now.
I7-860 (1156)
Evga P55 SLI
4GB OCZ PC3-12800
SLI GTX 465's (some 1GB models can have their SPU's unlocked to 448 (14SM total count)
Corsair HX/TX 850
And a MT/FT case of choice.
EDIT: And since the QPI is in place on the P55, you could even go with PC3-14400 or PC3-16000 and OC it up. But I imagine with the right PC3-12800, it could OC up to 2000MHz.
Ok, so I can clear some things up for you: You're most likely talking about a dual core AMD processor - Otherwise seen as an "x2" processor. No to be confused with "P(henom)II" which is the processors "family". Anyways, to build a good rig for gaming these days, and to remain future-proof, it's always a good idea to start with at least a quad core. Which for AMD would be seen as an "x4"
I suppose another misconception I should clear up is clockspeed.
Clockspeed is important, but should not be the primary determining factor. Look at the number of physical cores, and the number of hyperthreads (for Intel) For instance, the I7 (1156 and 1366) have 4 physical cores, but each core is hyperthreaded which means the core can do approximately double the workload. So, in the OS, the workload monitor (Task Manager for Windows) will show 8 cores doing work.
But even more important than cores is socket type. Right now, there are four big players in sockets.
AM3 (PhenomII x2, PhenomII x4, PhenomII x6) - AMD
LGA775 (Core2, Pentium Dual, Celeron Dual and a few others) - Intel
LGA1156 (Core i3, Core i5, and Corei7 (8xx)) - Intel
LGA1366 which is strictly Corei7 9xx for the moment - Intel
Socket type can give you an idea of recent the technology is. Unfortunately, it takes a little background knowledge to fully understand why each socket is different and why it is better for certain things over others.
There are several aspects of processors that are very important (though minuscule) to watch for and pick carefully. There are actually almost too many to explain in one post.