Germany's Windows Vista Magazine published New Assassin's Creed Screenshots with the maximum resolution of 2.560 x 1.600 pixels. Unfortunately Anti-Aliasing couldn't be activated in this resolution. But in the end nothing can beat this resolution. This is the second part of their ultra hi-res-gallery. The first part can be found here: http://www.windowsvistamagazin.de/?article_id=637478
Just click on the pictures until it pops up in 2560 x 1600 (about two clicks though).