I play CS:S and HL2: DM on my 20" with only 512mb of ram (so far) and the 128 MB Video Card. It averages around 90 FPS and is stunning on the 20" Display at 1680x1050. Its just amazing. Id go with the 20" stock ram, upgraded video card if you can afford it, then get some 3rd party ram. You'll be a happy camper.
hmm, i just find that more video memory isnt nessascary. i just want CS source to run nicley, and to hopefully run on high settings with no slowdown. CS:S is a big criteria for my mac purchase. 512 mb of ram will do but i'm going for a GB. 20" screen, SAME x1600 128 mb video card or 256?
I KNOW THAT THIS X1600 isn't a great card anyway so...is there a point?