I had thought based on reading posts here that the 2600k might overclock a bit better than the 2500k. It seemed to me that I read more people with 2600k say they had 4.9GHz or so and people with 2500k saying they stopped at 4.5GHz. Of course ymmv depending on your chip, your motherboard, and how long you want to fool with the settings. The 2600k is significantly more expensive, maybe the people that spend the additional money also have a better motherboard and also spend more time working with their overclock settings.