Re: 2x2 or 4x1?
it's memory controller dependant how well it works with 4 sticks compared to 2.
K10 and K10.5 CPU's can run in unganged mode (splits the 128-bit memory controller into two 64-bit memory controllers), which can increase performance with 4 sticks compared to two, since it can do multiple reads/writes to memory at a time, though bandwidth for each channel halves (but the total bandwidth won't change much)
Core 2 CPU's won't have much if any difference between 2 or 4 sticks. Some earlier K8 systems had trouble with 4 sticks, but the mid and later chips didn't.