Most modern engine control systems have enough timing authority to keep "premium fuel" engines out of detonation if 87 PON fuel is used, and manufacturers are getting away from their dire warnings of "engine damage" if less than the recommended octane is used.

New Corvette owner's manuals say that 91 PON is recommended, but NOT required. This is for the 6.0L 400 HP base engine, which has a CR of 10.9:1.

The new LS7 7.0L 500 HP Z06 engine's CR is 11.0:1, and the same applies.

What you loose is some power, especially at the low end, and fuel economy might be worse, especially in stop and go driving, but probably won't be affected at freeway cruise speed.

Duke