yeah- you can probably do that on 3x1920x1200, but who knows- what if you threw it on 3x2560x1600? you might start stressing it. It'll take a lot of pixels and intensive high quality graphics, but at some point it will run out of power:-) (hey- with the new Eyefinity 6 versions of cards- maybe it would stress it with 6x 1920x1200? lol)
I have two 5870's and play at 1920x1200, and I can't quite max AA in Crysis (I use x4), and it's still a little boarderline on FPS at times. I also can't quite max WoW. I also cannot max out Dragon Age Origins when using SSAA, but that's not a normal option to the game, but 4x SSAA looks better than normal maxed Dragon Age.
But keep in mind. I don't want to play games below 45 FPS anymore. If it goes below that, I will get motion sickness, and the game feels like it's lagging.