If you are still running a catalytic converter in your exhaust, stick with Toluene to avoid poisoning it,
and to stay safely on the rich side of full throttle air to fuel ratio.

Since your are using AKI from the gas pumps,
use a Toluene AKI of approximately 103

More AKI, RON, and MON is the table here

http://en.wikipedia.org/wiki/Octane_rating

Toluene can be bought at paint stores,
but it has been dropped from many hardware and big box stores because chemically knowledgeable terrorists can use it to create explosives.

xylene with approximate AKI of 105
is more commonly sold now
but does not burn as cleanly as Toluene.

If you are going to try to get increased detonation resistance from alcohol,
go with a
water / alcohol spray system on the intake,
as it will also cool your air
and increase oxygen content,
and boost both effective AKI
plus net horsepower.

Engineering wise
it is an extreme waste
to mix alcohols with gasoline in the tank
when those alcohols could have been
mixed 50/50 with water
and sprayed into the intake only at full throttle.