Arma 2 does support Crossfire. Just google it.
You have Crysis 3? Pretty amazing since the game is not released until Tuesday.
I have not seen the benchmarks on Crysis 3 yet but Crysis and Crysis Warhead were amazingly demanding in their day. To the point that even the newest hardware could not max the games. Crysis 2 looks great but was not so demanding on the hardware that was newest when it was released.
Metro 2033 is a beast if you just want to see how good your system is. It's the only game I have played so far that I have to turn way down to make it perform well on my 2 1/2 year old GX 460 1GB at 1920 x 1080. The new game Metro Last Light should be out in March.
Far Cry 3 is also very demanding.