Core speed bouncing back and forth from 2.4 to 2.8

SpeedStep uis kicking in during periods of light CPU load. It drops the internal multiplier to 6. FSB freq X 6 =2.46 GHz.

SpeedStep, is trying to lower the clock speeds of your CPU when you're doing nothing - it's one of intel's built-in features to lower power consumption and heat when you're not really "pushing" the processor.

You can disable this in the BIOS should you want your CPU's clock speeds to remain at a fixed number.

Trying? It is lowering the clock speed. And once you settle on a stable overclock, there's no reason to disable SpeedStep.