The opteron should easily clock as high or higher than the FX60. Do you use the memory divider/HTT divider to keep those 2 factors within spec? You shouldn't need any voltage increase to get 2.6 - 2.8 GHz. I've had an ASUS A8N-E mobo that wouldn't overclock worth crap, but 2 cheap boards (Asrock 939 dual sata and Biostar 6100) that get a 170 to 2.8 GHz easy.
If you really can't clock it up above 2.4 GHz, perhaps wait for next generation stuff as others said, though it is your money, after all. A socket 939 opteron @ 2.4GHz is still decent, if you have tight memory timings.