Check that out, that only $5 more than what you listed and has the 512mb bit bus! im buying two of these suckers and crossfiring them on a X38 P5E mobo with a Q6600 its really a steal of a deal $330 for two and think one 8800GT costs that much! not to mention these can be Flashed to XT verisons very simplyy then OC'ed more with the right PSU of course!
Simply the 2900PRO has my win even over the HD 3850 256mb when it comes down it the 2900PRO will more than likely win due to its higher memory and potential clock speeds.
I suggest you hop on that or get a HD3850 remember the 2900PRO require a hell of a lot of juice make sure you can supply it! if not then the HD 3850 is right up your alley.