Upgrade CPU?

I have a computer with a Procomp BST1M-E motherboard installed and a Celeron 700 CPU. I need more but I am not ready to buy a new system or change the motherboard for the moment. What is my best option? Overclok? Pentium III? Celeron but at higher speed? This motherboard is not very recent and the company stopped producing them, so the manual which is quite old claims that it supports Pentium III up to 733mhz. My feeling thou is that is due probably to the fact that at that time there probably was not any faster Pentium III, and also I have now the latest BIOS available for that motherboard and maybe now it will support a faster than 733mhz CPU. This is a link to the manual if anybody is interested: ftp://61.220.120.253/download/bst1m-ma.zip