You might also check the rebates. Often they can only be used once, so you would get one 2x1 set of $40 and the second for $80. At $120, that's still cheaper than $180 for the 2x2 set, but it does make the choice it closer. You might also check on other differences, like the make of the IC chips. If the 2x2 set uses a better IC chip, like the Micron D9, then the 4x1 set would use, then the 2x2 set would have better response to overclocking.
Agreed. Those Micron chips are legendary.