Id go only 1 GTX, at that res you wont need sli or gtx2. Then if some games come out where youll need it, go for the secong gtx, at a lower price. The single is cooler, can oc better, and in SLI it slightly outperforms the gx2
For crysis you'll need the second gtx to play it at reasonable framerates. Dunno about far cry 2. It's not based on the crysis engine so it's unclear how well it will run.