You mean processor clockspeed?
Well, I have currently 378 MHz Celeron, originally 300MHz. It was running at 450 MHz until recently when it started to act unstable so I was forced to lower the clock speed.
I ordered new CPU and motherboard yesterday, AMD Thunderbird 1400/266 and Asus A7V. I also ordered equipment for watercooling so I think I might be able to push it up to 1600 - 1800 MHz speeds

When you uprage, upgrade enough!