ok then you may want to ask other people because well, i have never used an ATI video card, only NVidia but from reviews in several magazines and over the net, 2 1900xtx if you are planning running dual monitors but if you decide to skip on the dual monitors, 1900XTX would be fine if you play less graphics intensive games, because even an 1800 will max out ah2 on settings and get 60 plus FPS w/ 4x AA (my lil 6600 AGP will run it at max 50+ FPS @ 1024x768 with 4x AA a low resolution but still.) If you are planning 30 in Dell or apple displays(2500,1600 [those are the large numbers, its just the numbers i remember]) 2 1950xtx in crossfire, of 2 7950 GTX in Quad SLI is a must becasuse that is HARD to draw..
(NOTE as you probibly already know AH@ does not support HDR to the fullest extent of my knowledge and as i have just recently learned ah2 automattically applies AF, so forcing it only makes it look a lil worse. BUT as for AA you could if you wanted to go 16x AA and it would look great but w/ bad FPS 20 or so.. or if you want to get 2 7950's you could make it run at 32x SLI AA.)
the only thing i dont like about what you want is 939... AM2 supports DDR2, the newest FX and the new AMD Athlon X2 5000+ are only supported on AM2 boards plus 939 is going out of style (all i mean by that is that it wont be cutting edge or preform quite as well.) and it may preform just as well, but youll be yearning for cutting edge, if your like me.