at stock, the radeon has higher bandwidth, so will be able to sustain higher fillrates than the Geforce (theoretically - and, it appears, in practice too). (166mhz DDR on GTS VS 183mhz DDR on radeon).
Geforce has higher fillrate - 800mpixels/sec + 1600mtexels....
Radeon has 366 mpixels/sec + 1100 mtexels....