No-tune mix

[Dust]

I have a 660cc engine running 12-14 psi of boost. The IC is a top mount inter heater, and I can feel the power drop as the car gets warm and the traffic slows. I have installed an injection kit to cool things down, and have not yet decided on the mix to use. I have been told that 12-13% is the range in which the water and meth kinda even out in flame front advancement and retardation. I have access to up to 50% methanol for semi cheap, after that it gets expensive fast. What is the recommended % for those not looking to tune, just to cool things off and make more power.

Tuning for the platform would be very expensive as it's not a "peformance" car, just something I want to toy with while I am in japan.