I disabled crossfire to rule that out and it effectively lowers my performance by half which makes sense.
My main gripe is that in non intensive areas, the frames move up and down quite frequently from 60, 51, 58, 57, 60, 57, etcetc. A perfect example is when on my LGV roaming through The Dunes, facing certain directions and I'm blazing at 60 capped, nice and smooth. I then pan the camera to face what is effectively the same type of rendered scene I was just looking at, and now it's down to 45, bouncing to 55, 41, 49, 52 etc.
I only get cap frames solidly while indoors. Combat indoors of course can get a bit heavy with all the particles, but even then, it's still fairly strong at 40-50+
So it has something to do with rendering outdoors. I did notice that if I yank the draw distance back to 100m(which is nothing), the performance is locked. If I move it just beyond 100m I start getting the up and down frames again.
My previous GTX 680 SLI handled the game fine anywhere other than heavy battles and populated towns, so needless to say I am not impressed with the lack of performance by the 290s in what is meant to be an AMD optimized title.
) but now i see each strategy and boss fight pattern (well only the one in BWA is tricky) and also i didn't had to roll for the 2 HMG (laser and plasma) for my Rhino and Mammoth for Lv25 
also one fun thing Campaign Mission are adaptive 1 player : less mobs than if 2 3 4 5 player, perfectly soloable even with a Nighthawk (well reflex unscope close range shot are a bit tricky to get right but "die hard learn hard" )
(they aren't worthless at all, only player who can't do anything else than popping turrets and AFK'ing thumping and can't adapt say Bast are worthless now)