The raciest version of BMW’s executive sedan has a little secret: push the programmable button labeled “M” on the steering wheel and unleash the full fury of the M5’s exclusive new V10 engine. One hundred extra horsepower come tumbling out, the redline skyrockets to more than 8,000 RPM, and a heads-up display appears on the windshield so you can keep your eyes on the road rapidly diminishing under the deep front air dam. The transition from sports-luxury to Nürburgring-conquering monster is as seamless as it is profound. The M5 has enough programmable settings for the active suspension and electronic driver’s aids to keep every teenage computer geek on your block busy for a week, but what really matters is the ability of the big M5 to hustle from point A to point B faster than nearly anything in its class (and a few cars higher up on the food chain). It’s another engineering triumph from BMW Motorsport, and one that really needs to be belted around any of Forza’s exciting tracks, like Germany’s formidable Nordschleife circuit, to fully appreciate.