I think the 5200Ultra is decent, it is better than the the GF4 MX series and the 9000/9200 collection, although that doesnt have the Ultra at the end of it, so I would probably give it a miss unless planning on overclocking it the full mile - the price is alright thouhg for what it is, but if it where the Ultra it would be something I would buy if I where looking at that range anything significantly better is also significantly dearer and although I havent seen a direct comparison with the 9100 I would say its on par if not edging performance on it.
I would personally steer clear of the 5600...the Ti4200s replacement seems to be doing a bad job of exactly that - it performs pretty much on a par with it, yet lags behing in numerous tests.