Water/Alcohol Injection
Methanol injection works, but it is not a cure all.
Generally methanol injection is used under boost to cool a charge. Running methanol injection at part throttle all the time will require a good sized tank.
So called "water" injection systems can not fix a compression issue, and were built for use under boost. Running straight water all the time can be hard on an engine as well - corrosion & pitting in the chambers & cylinders.
Double check your AFR in the "ping" range. Buy / borrow a datalogger like an LM1 with an O2 sensor to be sure this is not just a transient lean situation.
As for mixing race gas to reach 95 octane - I prefer to use toluene. 2 gallons of toluene in 10 gallons of 91 pump gas takes you to the 95 octane level. Toluene is a great booster, because it is very resistant to detonation. It is also widely available, and a couple of sealed 1 gallon cans in the trunk for backup is easy enough.
Running a water / methanol injection system can have a benefit. But you should be running that when the secondaries are wide open, not at part throttle.
Good luck with your project.
B.