From what I can tell there is no difference. I read a review at AnandTech about the AMD760 chipset and they talked a little bit about the 133Mhz FSB CPUs. Here's what they had to say:
<i>The <b>only</b> thing that sets the 1GHz and 1.2GHz CPUs apart from their 100MHz FSB counterparts is their clock multiplier. While the 100MHz FSB Athlon running at 1.2GHz has a 12.0x clock multiplier (12 x 100 = 1200MHz), the 133MHz FSB version only has a 9.0x multiplier (9 x 133 = 1200MHz). Obviously if you have a motherboard that can get around the clock multiplier lock this won’t pose a problem to you, but if not, then you will want to make sure that you only use a 133MHz FSB CPU on an AMD 760 board.</i>
the rest of the article is here: <A HREF="http://www2.anandtech.com/showdoc.html?i=1344" target="_new">http://www2.anandtech.com/showdoc.html?i=1344</A>