AceBandage is a good guy*. We just got a recent super influx of (no offense intended) Junior Members who aren't used to the particular conversational style of NeoGAF (you've been totally good with this, imho) and who tend more towards believing as truth every rumour of late they hear (which is understandable, but the presentation is often along the lines of that "When will this FUCKEN company learn?" meme). So people tend towards reactions of "Oh gawwwwd noobs!".
As I mentioned earlier, the only rumours about the Wii U GPU have been concerning GFLOPS, which is only one of several important metrics. However, this is what we've heard here and there (none are actual quotes):
A) From an AMD engineer or a press release or something that we really need to track down again, "The Wii U GPU offers greater than 1 TFLOPS performance"
B) From ... somewhere, possibly wishful thinking, "The Wii U is expected to be good enough to run the Samaritan Demo at 720p" (this would put it around 1.11 TFLOPS)
C) Recently, like less than a week ago, somebody of import suggesting a particular RADEON series which happens to be ~960 GFLOPS (might've been the Radeon HD 4770,
looking at Wikipedia now, but fook if I know!)
The Xbox 360's
GPU does 240 GFLOPS. Your 5670 does 620 GFLOPS. In this particular metric, if the above rumours are true, then the Wii U's video chip
in that specific metric would be between 4x and 4.63x the Xbox 360's Xenos chip's performance and between 1.55x and 1.79x your video card's performance.
My entire post, of course, falls completely apart were there a downgrade or had Nintendo not actually pursued a GPU of that general performance level. My intuition suggests they could reach that level and still stay within a very comfortable power/heat range, especially since they didn't supercharge the CPU.
* I assume guy.... I never checked under the kilt