Here's some unnecessary info:
Helicopter and airplane engines are run very different than car engines. They generally set the throttle to 50-80% and it only changes when they hit a particular pitch by using throttle curves (attached to collective on helis). The fuel is designed to accommodate that type of use. There is no need for a crisp low-end throttle response and there is very little chance of "loading up". The low nitro and heavy oils are there to protect an engine running full-time at high rpms. I can explain further but it's really unnecessary...
Just get a quality 20/25/30% nitro that's made for cars and don't look back. Seriously.