512MB VRAM is the minimum these days. Do not get a modern GPU for gaming that has less than 512MB of VRAM. 256MB restricts performance too much. It's like having too little RAM and having your HHD thrash and watch performance drop. Except with low VRAM, it has to swap data when it's full which drops performance like no other.
For ATI cards, 256MB is enough for resolutions up to 1280x1024 and even 1600x1200 on non-demending games. For Nvidia cards, 256MB will cause it to choke and die above 1280x1024. A 256MB HD3850 will kill a 256MB 8800GT, you MUST get the 512MB 8800GT or look for something else. Putting 256MB on an 8800GT is blasphemy.
However, consider the ATI HD 4850 too,it has a good price and performs better than a 8800GT
It's a very interesting article. Not only does it show how badly 256 meg bottlenecks the GT, (even at 1280 x 1024 in a few of the most popular game titles) it shows clearly how useless the over-priced 1 gig cards are as well.
I have the 256mb version of the 8800GT. I love the card.
I only run at 1280x1024 so its not a big deal.
From the benchies I've seen the 256mb runs neck and neck with the 512mb card up to 1280x1024, anything above that and the 512mb card starts shining.