If aviation gas or a nearby source of racing fuel just aren't good options for you, or if you just feel more comfortable running some lead in your fuel, this is the only product worth spending your money on - if you can still find it - Kemco Octane 130.
Octane Supreme 130, 6-32oz.
This is real lead (100% real Tetraethyl) , real octane booster, illegal for street use, costly as hell. You can Google it and read about it. Last I heard it wasn't available anymore but this ad says it has been reintroduced. I have a case of it that will probably last me for awhile.
I have a bone-stock Plymouth GTX whose 440 motor just doesn't like 93 octane premium with 36 deg timing. A quarter bottle of this stuff in the tank at fill ups and it does just fine. Pour a whole bottle in and the aroma of the exhaust will bring back memories of the 60s although the EPA will hate you.
Personally I don't think the lead is needed for engine durability - but if you need a little more Octane rating this will do it.