Different oil manufacturers specify different oil ratios, but 30:1 with a synthetic is a good start for a road racer.

My oils of choice are Castrol A747, Shell Advance Racing or Elf HTX976. I'm running Elf in my 300 now at 30:1, and I was also using it in the CR500SM @40:1. Good as gold and smells lovely too.

The different ratios are because the 300 revs hard (up to 13,000), whereas the 500 is a lazy pig in the rpm department. The 500 also spends less time flat out.

Remember that if you're pre-mixing, and you intend to try different ratios this will affect your jetting. If you go from 40:1 to 20:1 it sounds like a safe bet against seizure. However, if you haven't jetted for the new ratio then you've actually leaned the air/fuel mixture because you've displaced the fuel with oil, but the same amount of air. So you could actually seize.

HRC recommend 30:1 (A747 or HTX976) for their GP bikes. Do it!