problem occurs in far cry 2. i get better perfromance using a single card than sli. the games stutters a lot in sli and isnt performing as well as it should be. but when i tested other games and 3dmark vantage i get petter performance in sli.
i've downloaded the latest drivers so that rules it out.
i checked tomshardware far cry 2 benchmark for 8800gt sli and they are getting way better performance than i am.
The P5N-D is, in a word, awful! I went from a 680i board with 2x 8800GT and 3Ghz C2D getting 3dmark06 of 15000, to the P5N-D and it dropped to 12000. Then I bought a P5N-T Deluxe (780i) and 3dmark went back up to 15000. I'd only swapped out the motherboards!
In short the P5N-D is very slow compared with the 680i/780i, and if you have SLi you should really look at a better mobo. Asus' 750i in particular is quite bad, I think the EVGA 750i FTW may be a little better but for around the same price as the P5N-T so I would avoid the 750i alltogether.
The other thing I found with FC2 is that it is quite stuttery with a dual core CPU in ultra settings. I moved to a Q9550 and clocked it to 3.4Ghz and now FC2 runs like a dream.