The 5750 is nice, but I'm pretty sure only the upcoming 56xx series meets your low PSU requirement, especially under load (since 57xx is ~15W idle, much higher load)
4670 was a definite low-power winner last time, and I'd definitely recommend the 5670 based on preliminary benchmarks like ATI Radeon HD 5670: DirectX 11 For $99 : Introduction - Review Tom's Hardware