i am not sure if this is correct or not, but i picture FSB as a pipe. i think FSB is similair to electrical current. FSB & current is like a metal pipe. a larger FSB or more electrical current is like having a larger diameter pipe, more things can go through.
and voltage is like the processor clock speed. so just by looking at FSB alone you cannot determine if a certain processor is faster than another processor even if it has a FSB twice its size. example: comparing processors by FSB alone with 400Mhz & 800Mhz FSB, you cannot tell which is the better one.
i should think about this analogy more, i'm not sure if it technically makes sense.