Smaller engine dissipate heat a lot more readily than larger engine. They simply have more cooling area per displacement. This is why thost little Cox engines really come alive with 25% nitro or even higher.

Your engine will run on 10% no problem, but like w8ye said, it will be much easier to tune and run with a little more nitro. If a reliable run is what you want with the GP 07, a little more nitro will keep the glow plug heated more consistently for better reliable run, especially in the air.