Re: 4gb vs 16gb
4GB is getting low these days id expect you would see a pretty nice difference in daily use. id say you want at least 6GB. I got 3 sets of 2x4GB g.skill DDR 3 1600 for $30 a set on thanks giving i got 3 sets to fill my board $90 for 24GB.
I love G.skill they seem to get it right.