If you want to know which chip overclocks more over its default voltage, you can't seem to go wrong right now with the 1700 cores, especially 0308-0310 and the DLT's, from what I have seen. I am building a friend a comp, and have a 0310UPMW from excaliber right now that does ~2 at default voltage. Haven't pushed it much because it isn't mine.
If you are talking about which one can attain the highest total clockspeeds, I would have to say I am not sure. Probably the 2400 by just a bit as far as average go, but I could be wrong. My opinion is once you hit over 2-2.2 or so with an AMD, you are gonna be rockin so hard you won't know the difference between 2.3 and 2.4.
Smithers