Overlocking that high would depend on the stepping code of the chip and that particular piece of silicon. Keeping it cool will help alot...in fact, I was able to reach a higher speed at a lower voltage than I could with air-cooling so I recommend it if you are willing to put in the effort and expense.
If your Abit BIOS is like mine on my KG7 (it should be close) I'm pretty sure you can see if not adjust the PCI:CPU ratio--3:1 or 4:1. If you are running at 120MHz fsb and have a ratio of 3:1, you are hitting your cards quite hard (40MHz). This is a judgement call, but I personally don't like to push them past 38MHz 'cause I fried a NIC and it subsequently crashed my OS.