The late 2009 27inch iMac uses 1067 MHz DDR3. I don't see 1067 MHz anymore. All I see are: - DDR3 1333 - DDR3 1600 - DDR3 1866 Etc Which one should I buy to upgrade my iMac from 4GB RAM to 10GB? My plan is to buy an 8GB stick and use the 2GB stick on the other slot. Not sure if my iMac has 2 or 4 slots. What would you guys recommend? I'm buying locally (on a pc shop), not online. Thanks.