Yeah Thoroughbred B's are the best thing since the ol school celeron 366's...
But yeah, the average overclock I've seen on them on good air cooling is 2400+. Anything above that is pretty much a praying game, and pushing the core voltage up over 1.8v is just asking for trouble, and in my opinion not worh the risk. You're also talking about 220+ bus speeds, so quality of RAM starts to become your second enemy. Not too many ram modules can do that without extreme heatsinks and awesome case cooling.
Granted, there will always be those freak monsters that will clock to 2.2ghz, but those are like in the upper .05 percentile of the batch runs.
Processor overclocking is always a shot in the dark. But the B's seem to be very good proven overclockers, and I'mma get me one from newegg for ~50 bucks pretty soon here. I'll post my results when I get them.