Just a quick note .. the octane of the gas will not change your airfuel ratio. This is a simple math function of a quantity of air and a length of time you keep the injector open (sic. specific volume of fuel) in your intake charge. I think I know what you are getting at though.
What you need to alter with the race gas isnt boost or AF, it's timing. The higher the octane the gas is, the slower it burns. You need to advance the timing to make use of this slower burn. If you cannot change the timing then using a higher grade gas will net you little, unless your computer is pulling timing due to knock. Higher octane gas, since it burns slower knocks less cause its a bit harder to light (really *basicly* speaking). I suggest using premium and building to that then treating your car to a couple gallons to 5 of good stuff to raise the octane enough to deal with any knock you might be getting due to higher temps while racing.

Racing gas is expensive and wont really get you a bunch, with the stock computer. But sut sure does smell good out the tailpipe =]

David