Ixbt-Labs has a chart where they have been tracking Duron overclocking potential. It is broken down by full week codes and speed grades. Just scroll down the page to the chart.
Looking at their chart, the two highest listings they have are:
AKBA0031UPCW Duron 650 potential 1050-1100
AKBA0036APAW Duron 600 potential 1000-1050
Week 27 lists at 900-950.
We all understand though that there is no guarantee each processor will reach the max, a particular week just increases the odds.
Check out the listing, it's informative.
