for most users, 2x2gb is the best choice. not only is it a little cheaper, but it's easier for your motherboard to control and OC with two modules rather than 4. there's an exception where if you want to bench the memories, only d9 chips can get extreme clocks or low latencies and only 1gb modules have good d9's. however, nobody benchmarks with 4 sicks on their mobo. it's usually only 1 stick, maybe two