25%-30% for racing, yes the tuning window is a little bit smaller, but the low end torque will be much better as well as throttle response, and you can run a "slightly" richer setting and still have the power. Also higher nitro can get you better mileage as you do not need as much throttle to get the speed, power needed to clear jumps, accelerate ect. 20% for bashing and playing. I prefer to break in on 20% as it is a bit less stressful. With the correct tuning I have not noticed any difference in longevity between 20% to 30%.