well you are lucky!!! You are not limited to just overclock with the FSB. Actually, It won't really matter which you get if you are going to unlock the chip and overclock, as most people just go to a lower multiplier and higher bus speed as this yields the fastest system. For instance
12*100mhz bus = 1.2 ghz
9* 133mhz buss = 1.2 ghz
The second option will yield a much faster system due to the higher bus speed. Equate 200mhz with 100mhz and 266 with 133 mhz. So if you are overclocking, get whatever you want to, if not, then get a 266 chip. Hope that makes sense.