The highest performing card I would recommend is a HD 5850 if you have a good quality PSU. If it is "generic", then my recommendation would be a HD 5770.
I believe the GTX 470 is equivalent to the HD 5850. But it consumes about 195w of power compared to about 125w of the HD 5850. I wouldn't recommend anything less than a good quality 500w for that.
The GTS 450 is the equivalent to the HD 5770. The limited reviews I've seen also indicates that it uses more power than the HD 5770, but can still be powered by a generic 450w PSU.