The HD4850 and GTS 250 are comparable as are the HD4830 and the 9800gt but the HD4770 belongs on its own level between those 2 groups and the GT 240 is significantly weaker than any of the other cards you listed.
I have the 4770, I overclcock it about 20% stock its 750/800 --900/975 when gaming. Its about the same as a 4850 this way , but there are some games the gts250 is just faster in. Its not equal to a gtx260, unless its in a screwed up system. lol
The HD4770 is only 5-10% weaker than the HD4850 so a 20% OC should make it a good bit better. Not quite up to GTX 260 levels but getting there I guess.
The GTS 250 is definitely the best card you can get between $110 and 125.