From the 3 PCs you posted:
SYX Venture SG-1020 E7500 2.93Ghz CPU 9800GT Video card $700
iBUYPOWER 939TI Core i3-530 2.93GHz CPU, GT 220 video card $670
CybertronPC CINN21202 E5200 2.50GHz CPU, 9500GT video card $670
The one with the 9800GT would be the best gaming system. The 9800GT is quite a bit better video card.