What's the problem with the HD5970?

I've been comparing it to the 690, and theoretically it is faster than the 690(especially in pixel rate, by 58%).
But performance wise, it doesn't even come close to the 690, but stays at 670 level.
Why is this?
Are there just not enough power connectors for that card, that it consumes 294 W already, but more like 350W should be the optimal power provision made for it?
Or is it thermal throttling? The card gets hot, as I've read in another thread.
Or anything else?
 
Solution
Its an older architecture with less memory on a smaller bandwidth.
Its specs dont mean much compared to real performance. Synthetic benchmarks really mean nothing as well.