yes nitrous is the power adder that doesn't mind compression. run what you want just remember to take 2 degrees of timing out for every 50 hp shot of the juice.
91 octane .. is ok IF the timing and plug heat range is correct and the fuel pressure!! If it were me, and fuel is avaliable.. I would add a gallon to the tank to be safe(er) and run the piss out of it!! I feel being on the safe side is always better to make the second pass...??