Unless your engine has greater than 10:1 compression its just a waste of money. Do a little research on octane. If your engine runs without detonating on 80 octane 81 wont give you any better performance.
The 150's have 9.2 :1 compresion ratio so anything you buy at the pump will work except for an Ethanol blended fuel which will eventually melt the piston and ruin your fuel system. Alot of the 250's have 10:1 compression I dont know what the 250 Dazons have, but 89 octane burns plenty hot and doesnt usually diesel or detonate at that ratio unles your timing is off or the gas is old. If you have milled your head and your compression is higher than 10:1 then an octane or lead additive is better than benzene based high octane fuel, at least for these alloy engines that is. If some one tells you that they get better performance from a higher octane fuel and they'er engine ran fine without it or its not a high compression engine, they are lieing. It maybe that the fuel was better but it aint the octane rateing.