I'm curious. What brand of ram did you buy? I believe some of the Corsairs cause the base 1600 MHz to fall to 1333 MHz.. Which is what you have ;/
I didn't actually buy the RAM, but it's Corsair RAM. It came with the laptop when I bought it. I got from our own MacRumors Marketplace several months ago. This RAM is clocked at 1333MHz and so far haven't had any issues.
http://www.amazon.com/Corsair-Chann...6GX3M2A1333C9/dp/B006DI9PG8/ref=cm_cr_pr_pb_t