here's the math and debate for ethanol.
http://en.wikipedia.org/wiki/Ethanol_fuel
"Ethanol (E100) consumption in an engine is approximately 51% higher than for gasoline since the energy per unit volume of ethanol is 34% lower than for gasoline"
and
"The higher compression ratios in an ethanol-only engine allow for increased power output and better fuel economy than could be obtained with lower compression ratios. In general, ethanol-only engines are tuned to give slightly better power and torque output than gasoline-powered engines."
the math:
lets make the assumption that octane content doesn't influence total energy output, but the amount of ethanol does.
in 100 units of "regular gas -87 octane", 10 units is maximum ethanol and 87 units is octane. because ethanol burns 50% faster, 10 units of ethanol is equivalent of 10/1.5 = 6.7 unit of octane
so total = 87 + 6.7 = 93.7 units of octane power for regular gas
same idea for other grades
89 octane = 95.7 units of octane power
91 octane = 97 units of octane power
93 octane = 97.7 units of octane power
so overall increase from gasing regular to high end premium (93) is 4 units of octane power, which is 4/93.7 = 4.3% increase in overal fuel power
from experience, regular gas runs me about 600km per tank, and i noticed a 20-30 km increase when i run 94 premium, that's 3-5% increase in MPG.
so if premium gas cost 3-5% more than regular gas, fuel up.
last time i'm in the states (2 weeks ago), regular is $3.89/gallon and $4.09 for premium fuel. That's $0.20/$3.89 = 5.1%
In canada, currrent prices are $132.8 for regular and $152.3 for 94 premium. This is 14.7% more expensive
So yes, US has it good.
also, ethanol additive in fuel is more of a recent phenomenon, which is standardized to E10 (10% ethanol) as of 2006. So what happened 10-15 years ago doesn't apply as gasoline composition has changed over the years. Plus, the earlier link for not using premium gasoline was dated 2003, clearly not reflecting the gasoline of today.
http://en.wikipedia.org/wiki/Common_ethanol_fuel_mixtures#E5.2C_E7.2C_E10
"Other common blends include E5 and E7. These concentrations are generally safe for recent engines that run on pure gasoline. As of 2006, mandates for blending bioethanol into vehicle fuels had been enacted in at least 36 states/provinces and 17 countries at the national level, with most mandates requiring a blend of 10 to 15% ethanol with gasoline."