Heres a comparison between the Athlon II X2 250 and the x2 6000.http://www.anandtech.com/bench/default.aspx?p=96&p2=28
Since the 240 is .2ghz slower than the 250, the 240 would probably perform very similar to the 6000. If your deciding which one you should get definitly go for the Athlon II. Its newer tech, 45nm, runs cooler, overclocks much higher, so on and so forth. But if your thinking about upgrading to a 240 from a 6000 I would advise against it, its just not much of an improvement.