I am looking to add RAM to my iMac, which has the original 2x2GB and 2 empty slots. I am planning on 8GB RAM total, and here is what Im considering. 1. Add one 4GB stick, leave one slot empty for future expansion. 2. Add a matched set of 2x2GB. The price is about the same (matched set costs $3 more). I multitask a lot (Skype, Vent, WoW, iTunes, 3 Safari windows open usually). Which is a smarter buy?