I just want some feedback from people who actually have spent ~$400 on 4GBx2 DDR3 Modules on their MBPs. I am in a bit of a pickle: I definitely need a memory upgrade; but I don't know if I should buy a 2GBx2 or a 4GBx2. The 2GBx2 is ~$110 but if I decide I want 4GBx2 down the road, then I will have to sell my 2x2 and buy it. Any advice? Thanks.