Which do you think would be better - an hd 3850 512 mb, or an nvidia geforce 8800gt 256 mb? I'm guessing that even with the reduced memory, nvidia will kick the crap out of it, especially with aa and af turned on, but I'm not sure.
It will be as with the 8800GTS 320MB, after a while the performance will decrease as resolution and texture detail increases.
At certain resolutions the 3870 will close the gap and eventually perhaps even win over the 8800GT.
A fast card at low resolutions is great but if you plan on going 16x10 and higher more memory is preferred.
Some titles like GRAW2 and newer ones require 512MB to go max detail even at lower resolutions, not that "just" high detail with everything else maxed out looks bad...
For me it's a better toss up between 8800GT 256mb and 3870 512mb. Price also has alot to do with what is "better". I think if you had a single card I'd go for the 8800GT. If I was to go SLI/Crossfire I'd go for the 3870, mostly because ATI cards seem to scale a little better, and you can put them on an x38 chipset board which already supports pcie2.0 and 45nm CPU's.....plus I like red cards.
Also I'm not so sure that the 780i boards coming up will support some 45nm processors because they are just finding out that the 680i doesn't work with them all. The 780i is just a 680i with an "accessory" chipset which allows pcie2.0.
However if Nvidia officially(ever) releases their SLI technology to Intel chipsets then I'd go with Nvidia cards all the way, all the time.
Stay away from 256mb cards. If the 320mb gts was anything to go by, anything less than 512mb will really hurt dx10 performance. The 8800gt is too good to be glued to just 256mb graphics memory. If your looking to save money, I think the current 512mb 3850 has a good non-standard cooler on it, so you could concievably overclock it to a 3870 level. Honestly, isnt 256mb a bit measly these days/looking ahead at future games?