With nitrous, octane becomes less important. Nitrous cools the charge enough to fight detonation. But it also accelerates the burn. This is why we pull timing as we add more nitrous. You don't want peak cylinder pressure before the piston gets to top dead center on the compression stroke.
For a typical stock 350 with cast pistons, a 125 shot is safe. I've done 200 with cheap hypereutectics and the Jacobs' Mastermind progressive controller, on 91-octane. I set it for 50% at 3000, ramping up linearly to 100% at 6000. Very safe, since it was also pulling out spark advance as it was adding nitrous and fuel. It has adjustment for that as well.