After checking all the options in practice, we can state that the entire range of FSB frequencies up to 233MHz is working, that is, the mainboard is stable at any FSB frequency up to 233MHz. Overclockers should really enjoy it and continue the AMD's initiative about raising the FSB frequency of their Athlon XP above 166MHz. But at 166MHz FSB, the memory in MSI KT4 Ultra can be clocked only synchronously due to the restrictions in the VIA KT400 chipset. Moreover, the minimum divisor of the PCI bus that's activated at the FSB rate over 166MHz is 1:5. So, when overclocking the FSB above 166MHz, the system may lose some of its stability because of certain problems with the memory or expansion cards.