Every silicon semiconductor device is unique, and has different basic properties of electronics such as resistance, capacitance, inductance, impedance, and transconductance. 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, at the same temperature. Additionally, in a dual core processor, one core will always become unstable before the other. My 6600 is at 1.5125 vCore for stable operation with 52c full load at 3.7Ghz. I consider this to be the extreme vCore and temp limits.
Hopefully you'll receive a clean CPU that will be a good overclocker, but you won't be able to predict your OC until you actually try it out. As has been said, you should be able to reach at least 3.0Ghz, but the FSB ceiling of your motherboard will be critical with a 9x multiplier.
Hope this helps. Good luck!