Remember that octane is the fuels resitance to "knock". Fuels with a high octane number have a slower burn time across the cylinder, thus the ability to run higher ignition timming. Lower octane numbers have a faster flame travel thru the cylinder.
Late model vehicles run lower octane fuels due to lower compression ratios, and lower emissions, thus less cylinder deposits.
Leaded fuels used the lead as a lubricant for the valve seats and to some extent the valve stems. Early heads quickly pound out the seats with non-leaded fuel as there is nothing to cushion the valve to the seat. Late model heads have hardened seats to help with the condition.