This is something you really need to study its simple yet also not as simple, first up if you start messing with the FSB then you start to strain other things like the RAM , what RAM do you have?
And if you really want to see a difference then going from 266 to 275 wont do anything at all , the real trick is to set RAM=FSB or 1:1 and from 266 to 300 would be a start , but to do this you need to know what your doing and how to get there.
I suggest you go read about overclocking and what it means because anyone who just tells you to start messing there without you even knowing what your doing is not the way to go.
I would be willing to help you with all kinds but you gotta do the work.
peace