My Duron 600 is at 1007mhz, 106mhz FSB, on an Abit KT7, KT133 chipset. I had to push the core voltage to the max setting of 1.85 volts (1.91 volts reading) and I/O voltage to 3.5 volts. It runs stable except when the room temperature reaches 85 degrees, (29-30 degrees C), which it's done twice this year.
I considered doing the voltage mod but the fine soldering looked too risky.
I also overclock my Geforce256 SDR card from 120 core/166 memory to 150/210 but I had to add ramsinks, upgrade the GPU fan, and I have to open the case to keep it at this speed. The Duron doesn't need the case open.