We already reported on the confusion about the DX 10.1 mode of Assassin's Creed. Now we present a huge review dealing with this matter.
As a base for our tests we used a system consisting of an Asus P5N32-E SLI motherboard with an Intel Core 2 Quad Q6600 processor and 2,048 MiB DDR2-800 memory. Since only AMD's HD3000 series and S3's Chrome 430 GT are currently the only graphics cards able to display the shader model 4.1, we used several different graphics cards. Those were: a HD 3870, a HD 3870 X2, a Geforce 8800 GT and two Geforce 8800 GT (overclocked to 670/1,700/970 MHz) running in SLI. Furthermore we used Windows Vista x64 with and without Service Pack 1.
Assassin's Creed 8800 GT vs. HD 3870: Due to Service Pack 1 and D3D 10.1 the Radeon is able to smooth more areas than the 8800GT.
DX 10.1 gives more possibilities to the developers when working with Anti Aliasing. As Rage3D already mentioned, the use of a Radeon HD 3870 and Service Pack 1 improves the visual appearance of Assassin's Creed. If SP1 isn't used, there aren't any differences between the Anti Aliasing capabilities of a Geforce 8800 GT and the HD 3870.