I dont think revolution will be as powerful...but it is going to definitely be a custom processor...360 has 3 general cores...ps3 has a weird infostructure...i think because of this they will not be as efficient...but revolution will have games in mind just as gamecube did.
then there is the gpu..which may just outshine 360's. Nintendo and ATI have a good relationship. I think nowadays with all the shaders and whatnot its going to be hard to tell the difference.
and thats another nice thing about gpu's they can be constantly updated till nintendo is finally ready to settle. What i mean is if some sort of new technologyoccurs within t he next six months then they can implement that without having to severely alter the whole system because it's its own entity in a package.