The 1600XT is slower than the X800 XT. The thing is, The X800 XT only supports shader model 2.0 and 2.0b while the 1600XT supports SM 3.0. Because of that, some games will not run on the X800 XT, but of course such games wouldn't be too playable on the 1600XT on anything above low quality
. On games that support both 2.0b and 3.0 (which is very few and you need earlier drivers as 2.0b was removed from latter ones), the X800 XT would be faster. In SM 2.0 mode, the X800XT is considerably faster.