I dont know your board but I guess it is using the VIAKT133 chipset. This chipset cannot do high fsb speeds (110-115max and sometimes only 102!!), you have only found the max for your chipset, not your Duron.
You have to change the Durons multiplier to get higher speed. If your board supports multiplier settings you have to unlock your cpu by using the pencil trick ( connect the L1 bridges).
If your board doesn't support multiplier changes you can still change the multiplier by connecting/cutting the bridges.