In my opinion 25% nitro is too high for that engine. That's more of a racing fuel where you need to get the absolute maximum power out of an engine. Running an engine on a high nitro fuel quite often means having to continue with high nitro.

Higher nitro content increases power, but also increases the heat generated by the engine, as well as increasing engine wear. It will also increase the amount of fuel you burn.

A 40 size engine should not need more than 10%.
Dennis-