I live in Yuma, AZ. One of the hottest places on earth. I run 91 octane.
About 6 months ago I put a Coolingmist water/methanol injection kit on.
I now run max boost on stock turbo (25psi), afr 11:1 tappering to 11.5:1 at redline (8000rpms), with not a hint of knock. I'm running stock ECU custom Dynoflashed.
I converted my IC sprayer resevour. I run 150PSI pump, 4.9 nozzle (which is around 6 gpm with the 150 pump). I have 660cc injectors. I'm right at 15% water/meth to fuel ratio. It's like running race gas all the time.
The 1 1/2gal resevour lasts at least 3 tanks, and I boost all the time.
If you run 91 octane and don't have water/methanol injection you are srewing yourself.