IT'S the M that's important in BMW when it comes to high performance.
The M Division - as BMW calls its motorsport arm - has created some of the most desirable cars of modern times.
With an ethos to develop racing cars for the road it has been making motoring legend for more than 40 years.
The cars are benchmarks, renowned for supreme engineering and the latest offering is an all new version of the one which has become the standard bearer.
If ever a model defined a brand then it is the M3 - a muscle machine with manners craved after by enthusiasts from all over the world since the first one arrived in 1986.
The new one - and the M4 coupe derivative - is the fifth generation and the most refined yet not as raw as its predecessors but packing much more firepower.
Don't think of them as a beefed up versions of the standard 3 and 4 Series cars but as models in their own right - engineered to the hilt with bespoke engines, an aluminium front end, carbon fibre roof and in the case of the M4, a carbon boot lid.
Then there's the characteristic power bulge in the bonnet, side vents in the front wings, four exhausts, huge alloys and optional aerodynamic splitters which add venom to the looks.
None of it is cosmetic but there for performance, shaving pounds off the weight and enabling the M4 to tip the scales at less than 1.5 tonnes - lighter than many a supermini.
The M3 saloon is a fraction heavier but lacks nothing in the power department nor in sheer exhilaration.
Both use a three-litre straight six engine boosted by twin turbos to 431bhp and revving up to 7,600 rpm.
There is masses of power on tap from 1,850 revs and with a seven speed dual clutch auto transmission the response is amazing, matching the might of the quickest BMW of all, the M6 coupe.
The 0 to 60 time is a breathtaking 4.1 seconds and that's half a second quicker than the last generation M3. Like for like the new car is six per cent lighter and three per cent more powerful yet, crucially the engine develops 38 per cent more torque and is 26 per cent more fuel efficient.
The acceleration can be brutish but to keep all in check there is a plethora of electronics. Grip, poise and all round handling are little short of perfection.
An adaptive differential splits the power through the rear wheels with a bias of up to 100 per cent and the suspension can be adjusted to suit. So can the weight and feel of the steering, the throttle response and the gear shift points.
It takes multi mode driving into a new dimension enabling a huge variety of control and for purists that is critical.
For those of a less demanding persuasion it just means a huge amount of fun and even when left to its own devices the car is simply awesome.
Go easy and there is a chance of getting near to the 34mpg BMW claims as the official fuel consumption figure but unleash some of the M machine might and it can drop to the mid-teens.
Overall we managed to average 22 to the gallon and that was on demanding mountain roads through the Austrian Tyrol where both the M3 and the M4 showed their potential to the full at altitudes close on 8,000 feet where snow is apparent all year round.
Emissions are 194g/km, incredible for a high performance car and little more than some family saloons.
With the standard six speed manual transmission both the M3 and the M4 are not quite as fuel efficient with CO2 up to 204g/km and combined economy of 32.1mpg.
A compelling feature is a feeling of being at one with the car. There is plenty going on around the driver yet the cockpit is intimate, sophisticated, roomy and well appointed.
Any degree of primitiveness which may have been done on earlier M models in the name of weight saving is long gone and the new pair are dressed as well as any other BMW.
Very comfortable sports seats - specifically designed for the new M cars - are a finishing touch and technical sophistication is all around, even in the finely crafted aerodynamic shape of the door mirrors - an ‘in your face' feature.
Forget flashy sports features such as flat bottomed steering wheels - these cars have proper round ones. Just push the starter button, fire up the engine and the resulting thunder leaves no one in doubt.
Prices start at £56,190 for the M3 and £56,650 for the M4 and extras can take the final price well beyond £65,000.
Carbon brakes (complete with gold callipers) cost £6,250, a head up display is £825 and the auto box is £2,645 which all helped to take the M3 we drove close to £67,000.
But that is in keeping with the rest in this league of super cars where models such as the Mercedes C63 AMG, Audi RS5 and Jaguar XF-R also ply their trade.
With the new M range now effectively split into after BMW changed the way it designates saloon and coupe body styles (the M3 is the saloon, the M4 a two door coupe) it is likely that the M4 will be the most popular thanks to its smoother image.
Come September an M4 convertible will be joining the pack and that will be priced from £60,745 but in whatever guise these are exceptional pieces of kit - even for those who expect the most from the self appointed purveyor of ultimate driving machines.