to me it comes to this break down, either a gts 250, an hd4850, or a hd5750
performance wise, it would be the 4770<250~4850(<~)5750
really they are all pretty close the 4770 is probably the weakest of the bunch, but also on the 40nm process so it'll sip power
next is the 250 or 4850 which are darn close performance wise, they're pretty much interchangeable, if you like nvidia or ati you could go with either one of these
finally you've got the 5750 which is dx 11 which is nice and also 40nm process so it'll be light on power heat just like the 4770, it's a tad faster then the 4850 and the gts 250, but also 20 30 bucks more,