Instead of replacing the Duron, do the following:
a) Go out and buy a decent heatsink/fan unit, something other than the stock AMD model. Read reviews at Dan's Data for good models. Also buy an 0.7mm mechanical pencil and some heatsink compound.
b) Remove your Duron 700 CPU from your system.
c) Take the L1 traces on your Duron CPU and close them by drawing from point to point with your mechanical pencil. For more information, search for duron +overclock +"pencil trick" on Google.
d) Put some heatsink compound on your Duron's CPU core, and put it back in the socket. Install your new heatsink/fan unit over the CPU, being careful not to apply too much pressure and crunch the CPU core.
You have now unlocked your Duron 700's multiplier, enabling what will probably be some pretty good overclocking. Back when I had a Duron 600, I could run it with a basic Alpha PAL6035 heatsink/fan at 9.5 x 100MHz (950MHz) or 7.5x133MHz (1GHz). On motherboards that fully support the 133MHz bus speed, this not only equates to better performance due to the bus speed, but the CPU also ran cooler due to the lower multiplier. This trick works great for all the older Durons with ceramic packaging.
Disclaimer: If you don't do this right, or bork your box, I am not responsible. This is hard to do wrong, but it can be done wrong if you don't know what you are doing or aren't careful.