Gonna replace my RAM.

I currently have 8gb of corsair xms3 1333 ram, going to switch it to 16gb of corsair vengence low profile 1600 ram. After I pop them in how long should I run memtest? Also, any other thoughts? Speaking of which, how do I OC my ram? It's 1600 but I'm almost sure it'll show as 1333. Thanks.

You don't have to run memtest really unless you are overclocking them past their 1600mhz rating and even if you do just test with Prime95 and see if you are stable. You can't really overclock RAM much on Sandy Bridge. When setting speeds to RAM you get RAM multiplier or dividers. You get increments, 1333 - 1600 - 2000 - 2133. If you overclock the base clock which you really can't but you can raise it from 100 to maximum 105, that will overclock your RAM and CPU a little bit.