In my 250 I run 32:1 with BP 93 pump gas with Klotz super techniplate oil. Smells great, smokes, but it's all cleaned out by the time I hit 4th wide open thru the field. Once it's warmed up, it still smokes a little, but revs right up, smells great. I feel like it's the perfect mixture of protection and performance. I have ran it at 40:1 before, but I just felt like 32:1 was safer and better.
When I raced motocross on a yz125, I used Blendzall castor oil at 50:1 with 110 octane. I would replace the piston and rings once per season and I rode ALOT!