Hi, I know my system can only handle 4 gb. but is it really better to buy 4gb so the ram is matched, instead of just buying another 2gb and then having a mixed set of ram? I'm planning on buying from crucial.... oh and doesn't adding ram to an existing system sometimes make it unstable? at least that is how it is with PC's I think. I think its the macsales site that says its preferred to by 4 gb set so you don't have a mixed pair of ram. I guess it is worth the extra $50 then huh?