OK then, since no one with a 1GB card bothers to do such dirty work, I do it myself. I rob the 5850 1GB from my gf's computer and install it into mine.
When I tried to run the official benchmark at DX11 all max 1200p 8AA, I got the following error message:
http://i1097.photobucket.com/albums/...ch/err_msg.jpg
By applying the trick I mentioned above, I could finish the official benchmark without a problem.
1920x1200 8AA:
http://i1097.photobucket.com/albums/...ench/1200p.jpg
1920x1080 8AA:
http://i1097.photobucket.com/albums/...ench/1080p.jpg
And the plot of the log files:
http://i1097.photobucket.com/albums/...bench/comp.jpg
During the benchmark I observed severe lag spikes, and such lag spikes are also shown in the plot. Personally I would not call such play experience *acceptable*, especially during multiplayer sessions. Anyone who still insists on 1GB cards shall make his own judgement.
As a side note, some review sites got the fps numbers *in game*. I also tried it myself with Fraps and got a much higher fps, because there are blank margins which significantly reduce the resolution.