XFirex 5870 Resolution Question

I put together my rig about 7 months ago. I am currently running i7-960 CPU with 2x5870s in crossfire. My setup is primarily used for gaming. I have read stuff around here about getting more out of the cards if I am operating at higher resolutions. I currently have a single U2410 monitor at 1920x1200. However, I have been considering the idea of selling it and getting a U2711 which would enable me to run at 2560x1440. I am looking to get the most out of my graphics cards as I can while still running games at max settings. Also, I'm not too keen on moving to multiple monitors because I do not like the gap between monitors while I'm gaming. Thanks for any input you may be able to provide! Since there may not be a clear-cut answer to this, I welcome any pros/cons that may be applicable.