I've read the *many* posts about this already on here and elsewhere but still can't really find a definitive answer. I have a mac pro with 4x512MB RAM. I'd really like to upgrade to 4GB total, but want to do it the best way performance-wise. My question is the quad-channel over-talked-about question..... If I leave the 4x512 MB chips in there and buy 2 1GB chips, will this still be the best performance layout? Or will it slow down the other 512 chips by disabling the quad-channel mode thing? It's obviously a lot more money to toss the current chips and buy 4 1GB modules, but for arguments sake, would this theoretically be any faster than 4x512 + 2x1GB? Thanks.