It's not that unusual to see the Athlons top out at 107- some are real good and get to 110-115.
Some possibilities:
Cache: it's somewhere around there that you have to lower to a 2/5 divider- in fact if I recall correctly, the factory 750's are the first with that setting (I can be wrong- it may be the 800)
Voltage: What voltage are you using? It may just be a simple matter of adding .1 volt.
You'r best bet, however, is to buy a GFD- allows you to change the multiplier up to 8, 8.5, 9 etc