The overhead of emulation is not just significant (more like huge).
The clock/core compareason could hold if xbox360 and ps3 code could run
natively on PC architectures, but you can see that even PC ports have severe issue at that, so nevermind emulation succeeding where porting fails (memory bandwidth is an issue too, and there's nothing to do about needing superpowerful hardware, in the event that emulation even
works).