More than likely it's the standard 1920x1080 full HD resolution.
Maybe a Dell ST2320L 23-inch model that was in some of the Dell Studio XPS 7100 bundles.
If you're a casual gamer you should be happy with that HD 6850 you have on the way.
THG article: Best Graphics Cards For The Money: January 2012
describes in general terms how the suggested cards perform.
Best Card For $150: Radeon HD 6850 - Good 1920x1200 performance in most games
Best Card For ~$185: Radeon HD 6870 - Great 1920x1200 performance, 2560x1600 in most games with lowered detail
Also, the size of the card and it's ability to fit in the case and the ability of the PSU to meet the higher power requirements need to be considered.