the p3,although 4.5x124=558,if you mo/bo dosent support 1/4 diveder at bus speeds over 100mhz,the 450 could become unstable.The cel366 overclocked to 550 will be at 100mhz bus speed.All pci cards would still be at their 33mhz standard bus speed,harddrives included.The Katami is a p2,with the 512k cache,correct?Anyways it would smoke a cel.