normally people tell you to search, you dont even have to, there is a thread about 5 down from yours thats about the pro's and cons of av vs race gas, search it and you will find a LOT of info, there has to be 20 threads in here alone on it.... here is some reading for ya, hope you got some time to read!
Which kit and what is done to his motor. If the motor is stock myself I would not run more then 16 -17 psi on 100ll. Unless he is running water meth injection I would feel safer running race gas. Again that's just my opinion.
I run 17psi on mcx nytro with head shim on 100ll
yeah, i have played with that calculator more then i can count. its not science, i wont push the limits of octane a spreadsheet showed me, but it gives me a good idea of where i stand for octane needs, not just dumping $$$ into the tank when you dont need it!