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