I let my wife drive the car. That was the real test, she has a very heavy foot and drives fast.
She drove out to the dunes and back without incident.
I've gone about 150 miles on the 30% ethanol tank. I think 30% has been proven to be the limit for this car.
As of this second, the mileage meter is reading 24.5mpg. I think that that's 1 or 2 mpg below what it would be on straight up premium.