Certainly the Wii U will be more powerful than the PS3 and XBox360, although the exact details aren't known.
Rumours:
1300 GFLOPS GPU at ~750MHz, similar to an ATI 4870 (i.e., around 800 shaders). PS3 RSX is at best 400 GFLOPS but isn't as flexible, Cell is 200 GFLOPS. 360 is 500MHz and well under half that figure of SIMDS (again, not as flexible).
CPU... multi-core and PowerPC is known. Maybe based upon Watson technology - i.e., Power 7. Most likely is a dual-core (eight thread) variant of the eight-core Power 7, running at over 3GHz (Power 7 scales to nearly 5GHz), thrashing the PS3 and handily beating the XBox 360. If it is quad-core it will be a BEAST of a console.
