The higher octane gas will not help you one bit except for preventing detonation and all that happens once that occurs. So just run high enough octane for your given boost level and timing.
You can make up your own race gas by adding toulene to pump gas and getting just the right octane. Toulene is 114 octane (there is already toulene in your pump gas) so just calculate quantities by volume. For 95 octane out of 91 pump gas you would want to add about 3.2 gallons of toulene to 15 gallons of 91 pump gas. With your setup you probably don't need much more than 93 octane.
You can get toulene from paint stores, Home Depot or chemical supply houses. Will cost between $3 and $8 a gallon depending on who and how big a supply you buy. Don't spill it on your paint and let it sit if you want nice paint.
