I've got a quad core mac pro and I'm looking to put more RAM in than the originally shipped 1 gig (2 x 512). I've seen all the helpful links for what chips to put in which riser, however I've also seen people mention keeping things in multiples of 4 or 2. I'm looking to put in 2 x 2 for 4 additional gigs, and keeping the original 1 gig. This would bring me up to 5 gigs total, but is it a bad idea to have 5 since that is an odd number? Or is it ok because it uses up 4 slots? 6 gigs might be a little more than I can presently afford/truly need. TIA!