In terms of general performance, it would be quite strange if the WiiU wasn't stronger than the PS360, for the simple reason that Nintendo wants to be able to offer the best titles that are developed for the competing platforms. And if you want to make that a smooth process, you need to offer some headroom performance wise, smoother the greater the headroom, obviously. If Nintendo offers an equivalent, but different, platform, then all ports will perform worse than on the original targets, because the peculiarities of the original target such as EDRAM, or SPEs or whatever isn't available. Having your own unique benefits doesn't help bring you up to equivalence for ported code, only for natively developed applications.
So how much headroom do you need in terms of bandwidth, shader power, and so on? Damned if I know. If I were Nintendo, I'd more or less copy the Xenon CPU but substantially increase cache size, and improve the CPU<->GPU interface, ensuring that anything that runs on a 360 will run (better) on the WiiU, but with minimal additional die area or power draw. The GPU needs to outperform Xenos+EDRAM, and the easiest way to do that is to use a modern AMD design (which AMD stated was the case in their press release), and use GDDR5 for main memory. This has the advantage that using a unified memory system, the larger cache of the CPU helps reduce CPU/GPU main memory contention, and the higher main memory bandwidth further allevieates the same problem. And of course, high bandwidth is rather more straightforward to take advantage of than local memory pools with specific space/utilization limits. (You could attack the problem with a combined EDRAM/improved main mem approach as well, obviously, but that doesn't seem worthwhile.)
The main message being that if you want to have porting being a smooth process, you provide healthy margins.
If we reverse the scenario, and postulate that the WiiU is generally weaker than PS360, then we immediately run into problems as far as ports are concerned. Not only do you have to wade through your code to find ways to cut down the processing requirements generally, but you also need to jump through hoops to try to compensate for specific features of the original target that is absent in the WiiU. In effect, you would have the "porting to the Wii" situation again, where you need to reprogram major parts of your application from the ground up in order to make a port.
So - what are Nintendos stated goals regarding ports/multiplatform titles?
