This is a comparison between a card which is roughly twice as fast in practice as Xenos with the current top of the range AMD card. Bear in mind that the next generation of cards are ~30% or better faster than the one shown here.
http://www.anandtech.com/bench/Product/179?vs=162
Bear in mind as well that many of the results here are CPU limited considering the scaling of Crysis vs other titles.
Tease.