Our jaws were left hanging by just how much power and torque we measured. No, that delta was in line with expectations. Not because of the 13-hp difference between 91 and 93 octane. Are Californians, with their watered-down premium, leaving something on the table? We wanted to know. BMW requires 91-octane fuel at a minimum, with 93 recommended, so we did just that, switching between the common forms of premium gas depending on which state you're in. BMW explicitly warns about engine damage from doing so, and while that seemed unlikely in such mild temperatures, using the cheap stuff would have been wildly out of touch with what an owner would do (at least until this M5 reaches its fourth owner sometime in 2036). The mere thought of pumping regular unleaded into this $129,595 intercontinental ballistic missile felt wrong. The differences likely would have been exaggerated by extreme summer heat, which exacerbates engine knock, but we sniffed out differences even with the engines huffing cool midwestern spring air. We performed acceleration runs, 200-mile fuel-economy loops at 75 mph, and dynamometer pulls, running each vehicle on two different fuels and completely draining the tanks in between. A Dodge Charger R/T with the Hemi 5.7-liter V-8 carries the flag for naturally aspirated engines. Ford's F-150 is America's best-selling vehicle and is equipped here with its most potent engine, the 450-hp EcoBoost twin-turbo 3.5-liter V-6. At the intersection of effortless speed and opulent luxury, the BMW M5 Competition squeezes 617 horsepower from its twin-turbo 4.4-liter V-8. The Honda CR-V stands in for a swath of affordable crossovers and sedans with its turbocharged 1.5-liter inline-four. To understand how higher octane affects acceleration and efficiency, we assembled a four-wheeled quartet sampling a broad spectrum of the market. In a vehicle averaging 25 mpg and traveling 15,000 miles a year, that amounts to a $354 annual surcharge for using the more expensive stuff. Premium gas tracked at $0.59 more per gallon than regular unleaded as of this writing. What automakers rarely say is what, precisely, are the benefits of paying for premium. Vehicles such as the Ford Escape and Mazda 6 are advertised with power figures made on 93-octane fuel, although both companies are quick to note that these vehicles will happily run on 87. Today's engines are so sophisticated that even mainstream nonperformance vehicles can benefit from running on higher-octane premium fuel. Downsized but hardly diminished, many of these shrunken engines are more powerful than their predecessors, thanks to turbocharging, variable valve timing and lift, direct injection, and the advanced computer controls tying these all together. The trend we're really living is the story of smaller engines working harder, in everything from family crossovers to six-figure autobahn barges. True go-anywhere autonomy will prove as elusive as finding satisfying vegan bacon. Electric vehicles are decades away from showing up en masse at country-music concerts, county fairs, and Tractor Supply parking lots. The trend that's changing the way America moves is far subtler than any good click-generating headline would have you believe. Where Liverpool, UK Price £38,475 On sale now Engine 4cyls inline, 1984cc, turbocharged petrol Power 345bhp at 5300rpm Torque 295lb ft at 2000rpm Gearbox 7-spd twin-clutch automatic Kerb weight 1557kg Top speed 155mph 0-62mph 4.7sec Fuel economy 32.1-33.From the July 2019 issue of Car and Driver. Seat Leon Cupra R ABT 4Drive ST UK specification More exciting than a Golf R or Skoda vRS, it’s a bit of a belter with a boot. And with standalone sub-brand Cupra set to swallow the fastest next-generation Leon in a year or two's time, it might also be the last of the breed. Just 150 will be sold in the UK, and given that the Abt pack is a £500 add-on that comes backed by Seat’s warranty, it’s an option buyers would be silly to ignore. Seriously interested parties should get their skates on, though. If you want a family car that’s fast, rare and a bit of a hoot to drive when undertaking more than just the school run, the Cupra R ST should be right up your street.