I think that after AMD makes them they test them to see what speed they will run at and just mark them as such. And since most will test considerably higher than the lower clocked Durons (600-750) they just mark higher-tested CPUs at lower frequencies because they still have to sell CPUs at those slower speeds. Does that make any sense?
So, I think it just comes down to dumb luck as to the quality of the CPU you get.
You could possibly hit 1Ghz, but possibly around 950mhz will be tops. I don't think any improvements were made in the 800 over the previous versions, and should not overclock much better than previous Durons. Expect 945mhz as the top, but you could get 1Ghz out of it.
I'm at 1010mhz witha core voltage of 1.91v. The multiplier mouldn't hit 9.5 at any lower voltage. I was wierd, no extra voltage was needed to go to 10. I'd shoot for 927mhz. This seems to be a very stable clock. only need 1.7v to get there.
There were only 25 respondants for the 750 and 50 for the 800 all the others had at least 200 respondants. 538 people responded for the Duron 600. 938 is a pretty incredible overclock average!
One guy claimed a speed of 1300 mhz for his 600 mhz Duron. He was using a 75W Peltier and ran the CPU at a staggering 2.5 volts.
My Duron 600 runs stable at 1008 Mhz (with the case open). Left it running for 3 days with zero crashes before I closed the case. With the case closed I had to reduce to 950 mhz for stability. I run at 900 to be safe. Some day I will get better case fans.