256MB version of the GeForce 8800 GT has had a first run of benchmark figures posted and it looks like it will be a tough competitor for AMD's newly launched 38x0 series cards.
Although the benchmarks are limited to 3DMark06 and HalfLife 2 Episode 2, it looks like the 256MB card is going to be yet another winner for Nvidia, it's really just a matter of how much these cards will cost and how soon they'll be available.
As long as you're not running your display above 1,600x1,200 or 1,680x1,050 this card should be a really decent performer, but it runs out of memory at higher resolutions once you start to enable filtering.
It also seems to suffer compared to the 512MB version when you enable filtering at higher resolutions, as without AA and AF, it performs within one percent of the 512MB card.
You can check out the benchmark numbers here