This is what Abit says:
With BIOS: LX6CLY
Date: 06/17/1999
1. Supports Intel Celeron 466Mhz CPU.
2. Fixes the password function.
3. Fixes the Y2K RTC function.
If that is the case I would say that you can get a slotket and Celeron 533 PPGA, and run it 75MHz fsb x 8 =600MHz.
It is possible (but I am not sure), that with the right Slotket, you can run Celeron 700MHZ at 75MHZ fsb, and have a 787MHz computer.