FX-51 is 2.2 GHz, the original Athlon 64 is 2.0.

Both CPU's have a built in memory controller (which was previous on the motherboard) but the FX-51 is dual channel while the regular can only support single channel DDR. Downside to the FX-51 is that the dual channel memory must be ECC, which is 10-15% more expensive than normal ram. That type of ram is basically for servers and paranoiacs. It's memory error checking it not that useful for desktop use.