Well, I've got no way to check, but is there a way to overclock the system bus on a PowerMac to 166MHz? Or is the motherboard not fun enough to allow such a thing?
Also, bumping the system bus to 133MHz on the new iMac seems like it would be very possible, given the fact that the internal RAM is running at 133MHz. Once people start feeling like their warranties are useless, I'd like to see if this is possible. The bump would be a nice speed increase for certain (especially with games).