MacBookPro RAM: CL7 or CL9

According to Apple your machine has the 1066 MHz CL7.

http://support.apple.com/kb/SP544

HOWEVER Like the other answers say, higher RAM specs are often backwards compatible with slower mother boards ("logic board" in Apple's case). So you could go with the higher speed/lower cost option and do fine.

But I'd say that having a shop with a well known return policy might be better. Check the fine print.