Your CPU has a stock front side bus speed of 333mhz, with a 9.5 multiplier. 333 * 9.5 = 3.16ghz
If your motherboard is only running at 266mhz FSB, you'd get 266 * 9.5 = 2.53ghz. So, you need to go into BIOS and adjust your FSB to 333, if your board is capable of it.