The only thing is, if you run the FSB at say.. 166MHz, then the PCI/AGP could be kinda out of spec right? I don't know much about the SiS645DX ratios, but I know with some 845D/E/G mobos, you can lock the PCI/AGP bus speeds. Also, if you get a 845G mobo, you'll usually get the 4:5 ratio, although not the 4:6 in the SiS645DX.
<i>Past mistakes may make you look stupid, but avoiding future ones will make you look smart!</i>