“I would drive down into the Foxhole flat out and the people in the back are screaming, ‘Oh mein Gott, mein Gott!’… I used to say, ‘Gentlemen, please, just call me Walter…’”

Herr Haupt doesn’t do formalities. Instead he calls you a wussy if you lift through the sweeper at the far end of Maisach airfield, the former Luftwaffe training ground that’s now a motorwaffe training ground, the M Driving Academy outside Munich. And then he slaps your back sincerely when you catch the tail just so, and later calls your sister out if you kill one of his orange cones.

A nine-to-five BMW engineer, in his younger days Walter was also a weekend race driver, and the infamous M5 ’Ring taxi cabbie where his exuberant sideways style earned him that nickname: ’Mein Gott Walter’, it still says so on his BMW company ID, hanging on an M lanyard around his neck. In 1995 he got a class win at the Nürburgring Nordschleife 24 hour race in what he still says is his favourite car of all time, the E30 M3. “That was with two colleagues of mine,” Walter reminisces. “We even won the 2.5-litre class, and remember, back then the M3 had only a 2.3-litre engine.”

That was over 20 years ago, and now Walter is 62 but you’d never tell. He looks 52: “Fast cars, they keep me young…”

And surround him with fast cars, his fast cars, and Walter jitters like a sugar-tanked kid, head snapping in every direction, arms flailing and fingers pointing out roll cages and spoilers, rattling out specs and water-injection idiosyncrasies without a pause for breath, and you almost expect him to run up to one of the cars and paste his face to the window and shield his eyes with both hands going “Phwoar!” at the speedo…

On the move Walter’s as frantic, squealing away around Maisach’s makeshift circuit in a brand-new M4 GTS from the out, his own heeds of caution yelled out to our group of Middle East journalists just moments ago now completely abandoned.

“There are only 700 of these in the world!”… just before commencing destruction of some expensive Michelin Pilot Sport Cup 2s.

The M4 GTS would do it to you, too. This is the best M car Garching’s made in years. If I had more experience with their early stuff maybe I’d go further back — I never drove the mid-engined Seventies’ M1 and only had a ride in that fabled E30 M3. Someone like Walter and a car as excitable as the GTS are a perfect match, and it’s easy to see his influence in the project. The M boys didn’t hold back, and perhaps the biggest eye-opener is how different the GTS is to the standard M3/M4. How much better.

Where the base car never manages to disguise its bulk, the GTS feels delicate; where the one gives nothing back through the steering the other one tingles in your hands; there you’re perched up on sumptuous leather sitting so oddly high, and here you drop into fixed buckets wrapped up in a roll cage with an Alcantara wheel against your chest and fabric door loops in M colours, and I really want people to start calling me Jo Winkelhock.

“The development aim for the [standard] M4 was to combine motorsport genes with everyday suitability,” says Walter. “But the BMW M4 GTS is a more emotional model, which is designed with racetrack use in mind.”

The cabin is decked out in lightweight trim panels, lighter centre console, carbon-fibre seats. The bonnet, splitter, roof, and adjustable rear wing are composites. That wing sits on machined aluminium mounts. The rear diffuser is carbon-fibre too, the muffler titanium, the brakes huge and impressive carbon ceramics even on damp roads. That adds up to 100 kilos shed, and then there’s the 75bhp increase in power.

“We had to use water injection in order to achieve those goals,” says Walter. The GTS is the first production car to use the system and Walter explains that, put simply, water is sprayed into the engine to help cool incoming air since colder air provides a bigger combustion, and a bigger bang means more horsepower. Five hundred in this case, from the 3.0-litre twin-turbo straight-six, at 6,250rpm. I only wish the shift paddles were sturdier seeing as they get so much use, because like every truly great M car the GTS revs and revs and revs.

The red line’s at 7,600rpm but you don’t even have to take it near there to hear the GTS’ intent. The engine sounds furious, like, rude. It spits, snarls, and storms off with a high-pitched metallic din and turbo hisses in wake. Hard on Walter’s tail I must’ve bounced it off the limiter a couple of times with late upshifts because I honestly thought it would just keep revving.

It has NA-like response to the throttle and seems to be on call no matter how you drive it, pedal-pumping or what. With all the driving modes to choose from, like the standard M4, the GTS works best with everything in Sport but the steering in Comfort, which is Walter’s recommendation, too. Sitting so low and strapped in directly to the car the 1,510kg quoted kerb figure seems too high for the GTS’ quickness — it’s got all those same excitable jitters all around this airfield just like Walter.

Previously he worked on the lightweight E90 M3 CRT saloon, and before that on the 2009 E92 M3 GTS. Based on the standard car’s 4.0-litre naturally aspirated V8 that old GTS took that to 4.4-litres and shed more than 110kg. Just 150 were built making it an instant classic — they went for $125,000 (Dh460,000) when new and they’re worth double that today.

This GTS too is destined for greatness. It has unique adjustable coilover suspension, and traces of obsessive engineering that always help elevate cars like these to iconic status, such as hollow rear differential output shafts to save weight. If Walter didn’t have to buckle to legislation in the car’s biggest market, the US, he would’ve gone further. “In an ideal world polycarbonate windows would have been my wish, which failed due to homologation reasons.”

Even with regular windows, thanks to America, the M4 GTS is definitely worth the premium over the standard car, to answer our original question, and it helps to carry the cachet of a 7:28min ’Ring lap time.

“I’ve done more than 5,000 laps on the Nordschleife and the number is growing every year,” says Walter. “If you really know this track well, you can evaluate a car’s character within a couple of laps. How is the performance of the engine? How precise does the gearbox shift? Did the engineers put the right emphasis on steering, chassis, brakes and stiffness?”

And they want how much for the GTS, $150,000? Bargain, especially since it’ll be worth twice that inside a decade as special-edition Ms tend to be. But that’s the wrong way to go about it anyway… For the collectors Walter has a final warning: “This is first and foremost a driver’s car.”