Expreview has an interesting review, they try to figure out how much memory the GeForce 8800 GT needs.
In our test, we want to show you which memory size is suitable for 8800GT. So in the test we have three 8800GT. One is Leadtek PX8800GT 256MB, Inno Geforce 8800GT 512MB and GainWard 8800GT 1024MB. Because GainWard 8800GT 1024MB is a factory Overclocked version, we flashed its BIOS, lower the frequency to 600/1800/1500MHz(Core/Memory/Shader).
Check it out over here, they tested in various resolutions and with and without AA and AF. The test results indicate the 512MB GeForce 8800 GT is the best choice because it offers a significant performance boost over the 256MB version. The 1GB version isn't recommended as in many benchmarks it actuallly lowers the performance, only in PT Boats: Knights of the Sea the 1GB version offers a significant boost.