People always seem to ask similar questions about the TSX. With a compression ratio of 10.5:1 on the TSX, I would not and have not used anything less than 93 octane.
My thoughts are:
1) If Acura mentions "Premium Fuel" only, it's probably there for a reason. It's not like Acura is making money off of you or anybody buying premium fuel. With the TSX, I've heard people using regular gas, which killed their gas mileage and performance. Purpose defeated...
2) Those of us, who buy Acuras know that they aren't exactly the cheapest vehicles to buy. My point being, we can probably spend the extra couple of $$ to stick to the manufacturer's recommendations and be at peace of mind