With a little bit of luck in the near future I'll be fitting a water cooler to my socket 754 Athlon64 3000 (2Ghz), with a little more luck, I'll be overclocking the thing to hieghts that with my old AthlonXP setup would be considered silly (AthlonXP 2000@1.6Ghz o/c'd to 2Ghz with water cooling).
I'd expect to get 2.3Ghz comfortably with the possibility of 2.5Ghz at a stretch.
In other news I overclocked my mothers 1Ghz T'bird Athlon system to 1.3Ghz with the stock cooler with reliable results. I love my hobby :-D I just wish that the stock cooler for the Athlon 64 was as well spec'ed for the job at hand, as the temperatures are well above what I'd consider wise for general operations.