From Bit-Tech, one of the few websites that uses ARMA 2 in its benchmark suite:
"In Arma II at 1,920 x 1,080 with 4x AA the HD 7970 3GB produced a mighty minimum frame rate of 66fps, matching the dual-GPU HD 6990 4GB due to CPU limitation (yes, from a 3.3GHz Core i5-2500K). This was 18fps faster than its predecessor and 16fps faster than the GeForce GTX 580 1.5GB - a 30 per cent improvement over the Nvidia competition. At 2,560 x 1,600 with 4x AA the minimum frame rate dropped to 41fps, but this was still an incredible 50 per cent faster than the GTX 580 1.5GB."
Some significant performance gains to be had. Also, it's interesting to think that the ARMA 3 demos were obviously run on current kit (I recall someone saying the Gamescon Machine was an I5 with a GTX580). If these new 7 series cards can push out more fps in the current engine, it could be a positive sign for people wanting to gear up for ARMA 3.