is the gtx 460 the 1gb version? the 6850 looks good out of that list.
in terms of performance i think the 2 gts 450s will have the best performance, followed by the 6870. the 2 5770s, gtx 460 1gb and the 6850 all have similar performance.
i would go for either the gtx 460 or the 6850.
this image shows some of the cards.