I am going to be getting a refurb i3 iMac soon and it comes with 2x2GB. Some sources say you get better performance when you install in pairs when it comes to memory. I was going to get one more 2GB stick and throw it in one of the open slots...am I going to suffer performance loss? Or will I just be running "not as well as I could if I had 4x2GB"? Any knowledge is helpful.