some of my engines have run really high meth percentages.
tho mixing alcohol with petrol is not top favoret for me, problem being your alcohol needs to be completly dry to mix with petrol and moisture in it and it won't mix. i prefer to use 2 fuel rails 1 with neat petrol and the other neat meth and use the ECU to control the percentage of whats injected.
the carrot for useing meth are the following.
its equivalent ron rateing is much higher than pump petrol its around 110

methanol mops up heat , the injected quantity allon with laten heat of vaporisation drops intake charge temps very nicely on boosted cars can be a pita on NA cars in cold weather tho.
you need twice as much but its less than half the price.
even on a std compression engine you can see good power gains even on NA, seen 15% gains on stock compression NA 16vs, with turbo cars it allows higer compression ratios, more boost, more spark and reduces issues of heat soack espectaly in drag raceing situations.
favoret mix todate is 49 % methanol 48% nitromethane 3% propolyene ( that'll give you a big power NA valver that can scare the 20vt lot )