The time has finally come to upgrade the machine I bought this spring. The plan is to replace the boot drive with a 256GB Crucial MX100. The original HDD will be going into an enclosure. I'm currently torn between getting a matched pair of DDR3 1600MHz CL9 1.35V sticks or going with a single 8GB stick leaving open the possibility of bumping to 16GB, if my wife ever takes it over for her photo editing (a real possibility 1-2 years down the line). The only thing I can't seem to confirm is the latency and voltage of the stock RAM. It currently has 2x2GB Elpida RAM. Based on specs offered by companies as Mac RAM, I'm inclined to believe it is DDR3 1600MHz CL 11 1.5V, but I'm not positive. Can anyone confirm this? If I go with a single stick, I'll leave one of the stock sticks in for a total of 10GB. I know performance is slightly better with matched sticks, but I don't think it'll be evident in day to day tasks one way or the other, and I know Macs have run unmatched pairs reasonably well since the PPC days, as I ran unmatched sticks when I bumped the ram on my old 12" PowerBook.