well, offhand, unless you're using extreme cooling, the latest 2.6 Stepping is a D1, and you can probably squeeze out 3.4ghz out of the chip, but it isn't likely to hit 300fsb with a 2.6C.
now, if you can find a 2.4C m0 or 2.8C m0 chip (Stepping codes SL6Z3 and SL6Z5 respectively), your chances...