"I was lucky enough to have three different CeleronII 600's for testing. The first two reached 675 MHz, but wouldn't budge any further. The last CeleronII I tested reached 900 MHz, which is phenomenal, considering that the CPU was rated at 600 MHz. Another bonus was that this Celeron was now running at a front side bus of 100Mhz ."
FULL STORY @ CHICKSHARDWARE (http://www.chickshardware.com/html/articles/celeron600oc/c600-1.html)