All AM2 needs is 1 module around 1000 4-4-4 1T and you have all the bandwidth and low latency the CPU needs, its also a lot easier to tweak 1 module due to less load.

C2D is just the same really, shorter pipes and a need for fast access latency, so you may find running 1 DDR3 module is the fastest option as long as the speed is huge and the overall latency real low.

All we need is 1T implemented on DDR3 and we should be good to go with 1 module benching IMO