Ok, 55C under load is great. Just put some AS5 and it should shave off 5-7C degrees from your full load temps. Secondly, do not switch heatsinks. I take it that this is an LGA775 processor. If it is, then the LGA775 stock heatsink is the best you can get for those P4/CD on that package. There is no better air cooling. What more can you ask for? 4700 RPM, Huge ass fan? One more thing. If your board doesn't come with a utility for changing heatsink speeds, then I suggest you add a fan controller, an inexpensive and then turn up the fan speed...that is what i did and my proc. oced to 3.8 GHz from 2.8 is now at full load temps of 59C on 4000RPM