I have definitely seen problems with the GT120 not working well enough at high resolutions - at big graphics display sizes - -
At the moment i am suggesting that the nVidia GTX 285 - though not a BTO option - with 2 DVI ports is a better bet-
The 4870 , the GT120 both have display port connections-
the GTX 285 has 2x dvi-
This is a moving target.