You will need a custom tune for each octane and power level you want.
Most people have these:
1. 87 octane performance
2. 87 towing (for towing anything heavier than 2500 lbs)
3. 91/93 performance
If you never plan on towing, you could keep the canned 87 towing. Or if you want to run 91/93 all the time, you could have the canned 87 performance, 91/93 towing, and 91/93 peformance.
There are a lot of good answers here:
http://forum.gopowerhungry.com/faqs-...de-my-evo.html
I'm sure I missed something...