I had the pleasure to drive the M4 a couple of days around Munich.
Although the car is a hand full for real traffic, it was a constant endulgement to drive. It feels so dexteruos and angry when you explore the high end of the rpm range, feel the but kick on gear changes and feel the rear axle searching for grip on serpentine back roads. This is not just a machine, it's a monster that's so alive!
A M340i will probably be the better adjusted car for reasonable people, but in this case, I would prefer to be a hooligan!