Having spent a week behind the wheel of the car in question we are not even remotely shocked at this claim as it was blisteringly quick.
Recently Car and Driver got a standard M5 Competition onto a dyno and on Monday, reported back on its findings. While the regular M5 makes 600 hp (447 kW) with a 4.4-litre twin-turbo V8 engine under the hood, BMW says the Competition variant is good for 617 hp and 750 Nm of torque. The dyno showed the hotter version of the sedan makes closer to 700 hp (522 kW).
After the test, the dyno showed 617 hp (460 kW) and 822 Nm of torque at the wheels. Horsepower ratings are reported at the crank, and a 10-15 percent loss is expected by the time the power makes it to the wheels. Knowing modern drivetrains are more efficient at keeping losses to a minimum, the magazine estimated output at the crank approaches 700 hp.