I have to ask -- what jumper are you talking about? I don't think there are any jumpers on the 8kha+ that pertain to cpu bus or multiplier.
I know this doesnt help, but its interesting: On my other system (p3 700 fcpga on tyan s1854) the cpu will NOT run at its default speed (700). It will only boot if the FSB is at least 112 (7 x 112 = 784MHz). Like I said, not helpful but interesting =)