I had a Prescott Celeron 2.66 that overclocked to 3.8 and it benched at about the level of a 3.4-3.6 prescott. System felt alot faster than my old 2.4C.
For addition to the list. I just worked on a Abit LG-81 board and it had a large array of overclocking options. Change the FSB, vcore, vDIMM, lock the PCI bus. The voltages were adjustable for high above stock. I used it in a cheap setup to upgrade later. It had a Celeron 2.66/533 and was...