I expect Xenos to be about twice as powerful as RSX in shader code.
Shortly, we're going to see a cut-down, somewhat simplified version of Xenos (R520 - about 26 pipes total, not unified, about 1/2 the shader power of Xenos) perform at approximately RSX levels in terms of shading power...
Not to mention that RSX has effectively about one quarter of the fill-rate or less, of Xenos (RSX can do 2xAA in the same time as Xenos can do 4xAA, and Xenos has effectively three times the bandwidth to work with on top of that).
Xenon can transmit 20GB/s of vertex data to Xenos, while Xenos can suck in, effectively, another 16GB/s of texture data direct from memory.
If Cell is delivering all the vertex and texture data (from XDR) then it tops out somewhat short of the 36GB/s that Xenos can use. I can't remember the figure - is it 20GB/s? Of course you can deliver texture data from RSX memory, too - but that eats into fill-rate rather badly.
etc. RSX is going to look very old by the time PS3 is released.
Jawed