Stock Performance

With F.E.A.R. you see a 33% performance diffence in favour of the 640MiB board at 2560x1600, however neither GTS is what you'd call playable at that resolution, indicating that more than 640MiB of board memory is preferable for the highest performance in this game with 4xAA applied, at least where G80-based boards are concerned.  It's worth noting here that Radeon X1950 XTX, with 512MiB, is decent at high resolutions, pointing perhaps to a ROP bottleneck or driver issue for NVIDIA here.

Zotac Overclocked Performance

Overclocked out-of-the-box, the Zotac is able to increase its 2560x1600 performance over the stock clocked hardware by ~16%. Performance at the lower two resolution points is increased to roughly match the 640MiB GTS, too.