Since I need to pull the trigger on a machine soon, and am tired of waiting for a a macbook pro, I'm thinking of buying the 27 inch i7 iMac. My question relates to memory configuration. If I buy it with the minimum 4 gig, I think that's 2 2 gig modules. Can I buy two third party (OWC or Crucial) 4 gig modules and add them, giving me a total of 12 gig, or would have to get rid of the original 2 2 gig parts? If it's possible to mix the 4 gig pairs with the 2 gigs, will there be any negative performance issues related to that? If I can mix them, do I need to worry about who I buy the 4 gig parts from? Lastly, any positive or negative comments on OWC or Crucial (or other suggestions) for memory in general? I apologize if that has been discussed before (I'm sure it has). I tried a few searches for the material, but came up empty. Thanks.