With a slight overclock it can get to the speeds of 4000+
It might be tough to go from 2400mhz to 2.4ghz!
Seriously though, the s939 chip can OC much higher than that. It is also a newer design, with better mem controller, SSE3, and runs cooler.
I have 2 754s, and one 939. The 939 is just better.
That is only true, if OCing. If stock, the 754 is on par.