So now we know the benchmark: the M235i sets the bar unexpectedly high for a car not meant to be seen as a proper M car. So how far ahead can a real one get?
The M4 presents as an entirely more serious proposition. It looks mean as hell and spectacularly purposeful with that bonnet bulge.
Inside, you can tailor your damper, steering, engine and gearbox settings to your taste and mood, and when you fire the engine, the deep, sharp bark that answers supports BMW’s contention that this motor is so modified as to be effectively new.
The M4 addresses the road in an entirely different way from the M235i. It feels merely convincingly rather than comically quicker than its little sister in the mid-range, but where the M235i runs out puff soon after its 5800rpm power peak, the M4 just keeps going, maintaining maximum urge past 7000rpm.
But the bigger difference lies in the chassis. From one place to the next, the M4 offers a different category of performance. Enormous traction and massive grip set the scene, but it’s the car’s ability over dips and crests that sets it apart.
In such circumstances and up to about eight-tenths effort, it feels nailed to the road.
However, there is a cost here, too, and I don’t just mean a firmer quality of ride. For those used to earlier M cars and their sweet, endlessly forgiving natures, the M4 is quite surprising when you start nudging up against the limit.
It’s not malevolent, but nor is it easy to drive this way. Inherently, it wants to understeer, but despite excellent throttle response, it is trickier than it should be to mete out the precise amount of power required to neutralise this trait.
Sometimes you’ll get it just right; at others you’ll either be handing control over to the electronics fairies or, if you’ve given them a tea-break, moving your hands further and faster than you might have anticipated to correct it.
Read the full BMW M235i review
The result is a car of serious capabilities but one that, when driven the way that M cars should be designed to be driven, might at times cause you to question its loyalties.
Which way, then, does the B4 go? Does it follow the mean and moody route of the M4 or the sweet path of innocence favoured by the M235i?
In fact, it seeks to split the difference, its proposition being to provide the pace of the M4 with the manners of the M235i. And it gets close to pulling it off.
Its cabin ambience is the classiest by far and its standard sports seats are both the best and best-looking of the three. There’s enough in here – Alpina logos, bespoke blue-backed dials and beautifully stitched leather – to make it feel quite different from the BMWs although I’d happily trade its small gearshift buttons for conventional paddles.
The engine is radically re-engineered relative to that in the M235i, the fitment of a pair of turbos being just the start of it, but it still sounds similar when it fires up and similarly quiet despite those meaty quad Akrapovic pipes out the back.
But it is a torque monster. It’s happy to rev past 7000rpm but it’s best in its mid-range where, working in conjunction with the best automatic ’box in the business, it provides progress as rapid as it is effortless.