What's your res?
I think it's only slightly faster.
It does use about half the power, and offers DX11, but tbh the card is too slow for that to even matter.
I think it's a performance side grade and a decent leap in power consumption improvement, probably not worth your time with cheap 40nm products in the used market.
Erm that was the 5750, I think the 5770 is about ~15% faster than the 5750.. Unless it's free if you're looking for a performance upgrade there are a lot of great used 40nm products right now that would be of better use for you imo.