It will work with four sticks just fine. You will definitely need some additional MCH voltage though. Depends on the sticks and your overclock as to how much. Of course, use the least you can to maintain stability. I've seen it take anywhere from 1.33v (two .04v steps from default 1.25v) to 1.41v with marginal sticks. Since you're open to getting 2x2G, it will probably clock better with two sticks than four. Additionally, some with four sticks find that they need an additional .05-.10Vdimm, though that's rare. Rarer still is the necessity to loosen timings if neither of those things work. Neither of these last two steps are needed in the vast majority of cases.

FWIW, if you are going that route, I'd stay away from Ballistix. At the abit forums we've seen quite a few sets get RMA'ed/returned/sold. It seems we may have the reason why as well. See this thread...more specifically this post, which is a copy/paste of a conversation with a Crucial rep. Long story short - they quit producing 16-chip 1Gb modules in favor of the cheaper (and less reliable) 8-chip sticks. No reason aside from it being cheaper. Quality apparently doesn't enter the picture as was essentially verified by the rep. Bear in mind, this is just my personal opinion and is based on that thread among other anecdotal evidence and I'm not speaking for abit or the abit forums (heh, nor do I have any authority to do so!). Again, just FWIW.