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.
I saw both cards you are discussing on there, and the one Newegg says is 256bit its link goes to a page that says 512bit and Sapphire's site only has one 2900Pro listed.
But knowing Sappires history, It very well could be 256bit..kinda like the 128bit 9800 Pro vs 256bit 9800 Pro, but you would think there would be more of a price difference....either way i say go for the one that says 512bit since its only 5-6 more