You decide what use you give the new XT4 and how much are you willing to pay. All of my GM vehicles use regular gasoline, yet one of them (1995 Buick Regal Limited with 3.8 L V6) was a great performer, running at 55 MPH at just 1700 RPM. During the annual inspection, its idle was as low as 650 RPM, and the examiner thought his equipment was in error! I sold the Regal after 21 years of service, and the new owner is still happy with it even as late as last month.
I never had to use premium fuel since GM engines are very advanced in detecting any knocking and never had trouble with them. So if you want to get the best cost/performance ratio, just use regular fuel, drive smoothly, save money, and get a very long engine life.