Just to let you know, some mobos have holes on them, not literally holes but strap holes.
There are mobos that you cant set certain FSB due to the Northbridge straps.
Like my mobo, it is unstable from 350~399 MHz, but stable at 400MHz as it changes from 1066MHz to 1333MHz strap.
So thats why I lower the Multiplier instead and increase the FSB too 400MHz.
So example. I cant get 350MHz x 9 Multiplier which is 3.15GHz but I can get 400MHz x 8 Multiplier which is 3.2GHz and is higher Frequency. Weird huh?
So try lowering your Multiplier and increase the FSB a bit more to achieve the clock speed you want. Besides, its better to have lower multiplier but high FSB.