(btw, I am talking of the famous Celeron 300 Mhz "Mendocino" which would run at 450Mhz, anybody remembers?) Anyway, still working fine at 450Mhz.

Oh, for sure. My main print server is still running that chip at that speed. Piece of tape over the pin (which one was it? B21? Don't remember) and you're golden. God, what a great hack. I even still use this as my animated Win98 bootup logo even though my desktop system has been long since upgraded. Note the piece of tape in the illustration.