be aware of, that the ZX chipset might not support 100MHz FSB - which does limit your choice of cpu's. (P3E is at 100MHz and P3EB at 133MHz FSB) But check the mobos specs. at producers homepage...
BTW your celeron 433 would likely work fine at 487,5MHz (6,5*75MHz) and maybe even at 6,5*83 - resulting in 539MHz - keep in mind that the voltage easily may be increased to 2,2volt.