This is not the first time we've heard that ATI's new chip will do free FSAA. A few sources confirmed that with R600XT, Radeon HD2900 XT there should not be a big performance penalty if you use FSAA and Aniso in games.
But of course there is a catch. The "free" FSAA comes only in low resolutions and it's possible thanks to fact that the 512 bit bus has a lot of bandwidth. At 16x12, 20x15 or higher resolutions don't be surprised if you see a big difference once you turn the FSAA and Aniso on versus the score without it.
The GDDR4 card with faster memory will have better performance than the GDDR3 version of the R600XT, as it simply has faster memory. So, again, purely marketing talk.