ram....what are you planning this system for?
if other than gaming, and based on mobo...
for example: mobo with 4 slots, get 2x2 now so that you can opt for 2 more chips later
if just gaming and never wanting to do more, you could opt to fill up all banks
personally, to me, no advantage in 4x1 in this scenario. Other than maybe getting the chips cheaper.
This is based on you getting 64bit and having potential use of up to 128g