Heres some information I found in a book I have.
Supercharging, Turbocharging, & Nitrous Oxide
by Earl Davis and Diane Perkins-Davis
pg. 116
Under the "Consider the following" on the page sideline.
"Each 25* reduction in charge air temperature reduces octane demand by 1 point."
There are also several other octane related points to ponder in the section aswell. If my stupid scanner was working right I'd just scan the page and post it.