All of these cards can play the UT3 demo reasonably well at this resolution, the 8800 GT included (TechReport: )

TechReport: We tested the UT3 demo by playing a deathmatch against some bots and recording frame rates during 60-second gameplay sessions using FRAPS. This method has the advantage of duplicating real gameplay, but it comes at the expense of precise repeatability. We believe five sample sessions are sufficient to get reasonably consistent and trustworthy results. In addition to average frame rates, we've included the low frames rates, because those tend to reflect the user experience in performance-critical situations. In order to diminish the effect of outliers, we've reported the median of the five low frame rates we encountered.

Because the Unreal engine doesn't support multisampled antialiasing, we tested without AA. Instead, we just cranked up the resolution to 2560x1600 and turned up the demo's quality sliders to the max. I also disabled the demo's 62 FPS frame rate cap before testing.