Throughbred 'A's are not good overclockers. On the other hand, Throughbred 'B's are excellent overclockers.
I'd be sure which you have. The Thoroughbred 'A' core was used on up to the 2200+ CPUs, the Palomino core was available up to the 2100+ level. Basically these two cores have essentially the same overclocking ability. The only real difference between them is that the Throughbred 'A' core will dissipate slightly less heat than the Palomino at the same clockspeed.
Personally, I'd stick with what you've got and if you really want to overclock, find a new Throughbred 'B' 1700+. These often overclock to over 2 GHz (sometimes as high as 2.4 GHz) true clockspeeds. Online, these are around $50.