Monitor?

Solution
You can go all the way up to 2560x1600 resolution, a single 5870 provided better than 40 FPS in all games tested except crysis when tested at max detail, but crysis at very high is a killer for most any system. There is basically no limit to how larger you can go, you can even run 3 monitors as one large one as long as their combined resolution doesnt exceed the cards max resolution.
You can go all the way up to 2560x1600 resolution, a single 5870 provided better than 40 FPS in all games tested except crysis when tested at max detail, but crysis at very high is a killer for most any system. There is basically no limit to how larger you can go, you can even run 3 monitors as one large one as long as their combined resolution doesnt exceed the cards max resolution.
 
Solution