A single HD7970 (or even a HD7950 with a good OC) makes the most logical choice. You won't be able to "max" out Crysis 3 but you will be able to push all the settings up and still maintain your target framerate. Heck I would imagine "maxed out" looks no different in motion to "not quite maxed out" yet has a high FPS cost. Note I run it at "high settings" (shadows on medium) @ 3600x1920 on a single HD7970 clocked to 1250/6400. My framerates as measured in the "Dam" level seem to hover between 35 and 45 FPS. Very High settings with some AA should manage better FPS than that at 1080p.