Of course just speculation on someone's side
Only the idea of 32 unified shaders for Xenon GPU and 32 pixel shaders for PS3 GPU could be accurate.
The idea of the embedded memory in the GPU for HD frame buffer rumored for Xenon GPU has been taken and used for all the consoles.
Also too much memory especially for PS3.
There aren't many differences.
According to this picture all the three consoles will have the same GPU except for the fact that in the PS3 GPU all the shaders units will be dedicated to pixel lighting (because as it's speculated all the vertex work will be done by the powerful Cell SPUs)
Then we would have Cell (PS3) > triple PPC core (Xenon) > double G5 (Revolution) on the CPU side.
You can see the memory quantities by yourself (absurd in the PS3 case).
Anyway it's not accurate,just speculation.