After much problems with my Duron 650Mhz that not wanted higher than 900Mhz.
I decided to swap to a 600Mhz and after that it was no problems
to reach over 1000Mhz.
here comes some results from my new Duron 600Mhz
that reached 1104 Mhz with a ABIT KT7 Motherboard
both now running with 512Mb Memory Cas 2-2-2