Planes are usually low nitro. Helis are higher nitro for a little extra power and more cooling (their load and cooling arrangement is usually marginal at best) but haven't seen much over 30% in the heli verse.
Cars can run higher nitro too. I still have a few gallons of some Byron's 55%/6%oil "drag race" fuel. I've ran that stuff in engines I normally run 20-30% in, and noticed very little difference. I now use that fuel just to add methanol and oil to produce multiple gallons of lower nitro fuel. The 55% just isn't necessary.