This is why research is important. If you thought a single 6950 would max out games with triple monitors, you're dreaming. Especially 3 1080p monitors. You could get a nice FPS improvement by going something like triple 1680x1050 flipped sideways or even 1440x900... 3 1080p screens is a LOT of pixels.
It's even more extreme than 1920x1200 to 2560x1600, but here's some examples of what happens:
As you can see the FPS drops quite a bit. Crossfire 6950 should handle it well.