The Coupes have the same disclaimers and make peak power with premium fuel. The ECU will adjust the knock threshold so old-folks can continue using the 87 water and save 3-5 bucks a tank.

➕1⃣ Quote of the day, the last sentence. You "age racist"...
And assuming a 7.5 percent decrease in mpg because not using top tier premium (because of the V6 and V8 detune for regular)... A 15 gallon fill, means an extra gallon lost for same miles driven using regular. Typical 30 cents difference a gallon for premium. $4.50 cost difference in a 15 gallon fill. With cost of fuel about $3 now for regular, seniors using regular save a net of $1.50. Which buys them a pop for the next trip to the MCL (MediCare Lounge) Cafeteria. If price of fuel goes back up to say $4.50, not any net savings. This formula works no matter what the mpg is for a 15 gallon tank fill. And many pure premium users have measured a 10 percent decrease using regular.
The 2012 V6 I rented for several months, prior to buying, has more power using premium. Using regular decreased its mileage by 11 percent.
The debate will never be totally settled.. Hyundai has considered its customers preferences and choices. And has programmed a motors that are designed to best be used with premium, to be used with regular.. Unlike some other brands. Kudo for Hyundai.
It has been reported that both Ford and Hyundai used premium (and the CPU had adjusted program assuming using premium all the time) in their EPA MPG tests.. Which were used for the public MPG rating. Because of the penny pinching youngsters, and MCL "their way or the highway" aged users used regular, they experienced decrease in mileage compared to what was published. This, combined with the rigged EPA MPG runs that can over estimate MPG, those motors that were designed for premium had a large decrease in the MPG ratings. This affected the Ford Ecoboost (which also allows the use of regular in a reduced MPG and power setting), and all Hyundai high compression (and turbo) GDI motors the most. Today, the MPG ratings are reported to be based on using 87 octane. Both Hyundai and Ford got in trouble about over rated mileage claims. Too bad the "lower" mileage they got in trouble for, many times, had more to do with using 87 octane 10-15% ethanol cheapo gas. Which is going to reduce MPG and performance in motors designed for peak performance and MPG with premium.
It is reported that Mazda uses regular for their MPG ratings in their sky active GDI high compression motors. That is why so many Mazda Sky active owners experience better than the average mileage when using top tier premium long term. As an example our Mazda 3 Sky Active will get well into the 42-44 MPG range on highway. Which is far above the EPA raring. And will average 33-36MPG in town. Which is also above the city rating. Mazda does not promote the use of premium. And power is rated using regular too. However, we experience not only better mileage, but better power using premium.. More off the line torque at lower RPM (where knocking and detonation can be heavy, where a massive detuning when using regular will happen), and better response when cruising in the uber low RPM overdrive gear steady state (again, can be a detonation and knocking magnet in this motor running range). This will also translate to better MPG when the CPU does not have to detune a high compression GDI optimized motor with premium.