TEST DRIVE: 2015 Mercedes-Benz CLS400 4MATIC. I love what counts as “slow” these days: “As you’d expect, a 3.0-liter turbo six doesn’t accelerate—or sound—like the forced-induction V-8. At the track, this example hit 60 mph from a standstill in 5.1 seconds, nearly a second slower than that comparison-test CLS550 but, crucially, equal to the Audi in that matchup.” I remember when a 5-ish zero-to-sixty time was unbelievably fast. Now it’s considered kind of slow — in a four-door car.