I presently have a Celeron 400 o'clocked to 500 MHZ using the 83 Mhz front side bus setting, on an Abit ZM6 (which is identical to the BM6, except for the minor differences in the chipset). Both the BM6 and ZM6 have the same FSB settings via the BIOS, which are : 66, 75, 83, 100, 103, 105, 112, 124, 133(1/3 pci divider), and 133(1/4 pci divider). You should be able to bring up your 433 celeron to 490 Mhz (500) no problem using the 75 Mhz FSB setting. You might have to increase voltage, but you shouldn't need to. If that works, then try 83 Mhz FSB (for a total 540 Mhz). Or, you can go out and buy a cheap 566 Celeron II which has a very good chance of running at 850Mhz, using the 100 Mhz FSB.