apparently farcry has problems with newer generation cards. Have you installed the 1.2 patch???
I wouldnt give up on that card too much. In every doom3 hardware review i have seen your card SHOULD be performing a hell of a lot better. maybei ts a faulty card??? Looking thorugh your specs it doesnt seem like anything would be causing a bottleneck. i dunno. i would say its a faulty card or something.
I would recommend to anyone to get the 6800, as i always have.