It depends on how you configure the XPS. Only the T7400 or T7600 would match that T7500 in the Asus. Graphic wise I think the 8600m might keep up with the 7900GS, but not the 7950GTX.
I want to use 2 extra tft with 1900x1200 resolution for one laptop. Can i use it with asus ? if yes, can i do it with dell 2407WFP ? Can this vga card handle 3 x 1900x1200 ? (laptop+ 2 external tft)