I understand there are no solid state devices 100% identical. Every piece of silicon is unique, and as such, has different resistance, capacitance, inductance, impedance, and transconductance properties. Although two consecutive serial number CPU's from the same fabrication, with the same stepping codes, may appear identical, they're yielded from different location on the silicon wafer from which they're manufactured, and like diamonds, each has it's own unique flaws.
Even though their dynamic operational characteristics may be very similar, no two CPU's will overclock to exactly the same stable maximum speed, at the same voltage and temperature. Additionally, in a dual core processor, one core will always become unstable before the other. The overclock ceiling for AMD 90 nanometer dual core processors is about 3.05Ghz with top-of-the-line air cooling. Among the Opty's and X2's, the 170 is statistically the highest overclocker, and is typically a good OC risk.