http://www.tomshardware.co.uk/GeForce-8800-GT-256,review-29841.html
Simply have look at this article. As you can see, if you play with AA and AF, the 256MB of the 8800GT can't cut it, and the 3850 takes the lead, without AA, the 8800GT is the fastest. It also depends on what res you'll be playing at, if it's 1280x1024 and above, get the 3850.
Except for the fact that the version of the 8800GT he linked to is significantly overclocked. It has a 700 MHz core clock as opposed to a standard 600. Which would probably tip it in favor of the 8800GT.