Any increases to the FSB is going to provide a larger performance increase (at the same clock speed) than just simply inceasing the multiplier. (FYI, Athlon 64's have a locked multiplier, so you're going to have to overclock by increasing the FSB).
So the short answer is this: 9x250mhz is better than 11x200.
If you've got a good motherboard and decent RAM, 250mhz should be attainable for a FSB.
-mpjesse