There should be no difference. Same GPU, same amount of VRAM, same memory bus, and as far as I can tell the same clocks.
Only real difference I can see.
The cheaper one has two DVI ports, one HDMI and one Displayport output.
The more expensive one has two mini-Displayport, one HDMI and one DVI.
Would go for the cheaper one, more useful display outputs (Displayport is the best, but only high end monitors support it).