I'm just waiting on my new 27" 3.4GHz i7 iMac to arrive. In preparation, I have been shopping around for an extra 8GB of RAM to add to the base 4GB. Should I be looking to get CL7 or CL9 1333MHz memory? I've read various answers but I'm still not clear about whether the latency timings makes a difference. Any suggestions would be greatly appreciated. Thanks!