I got 2.5 GHz (250 MHz x 10) relatively easily, but I decided to stop there so I could run my HTT at 4x 250 MHz. One day when I decide to mess with it more maybe I'll take it further.
Try the stock HSF first...those processors don't run that hot, especially if you're not going to overclock. I couldn't get my 3000+ to go over 39 C using stock HSF.