Never in Cars in Action's history has there been so significant a super test. Yes, we have tested certain of these three together already, their predecessors certainly in the past, and we will clearly run their descendants against each other in future, too.

But there is an historical significance about this one – a kind of never to be repeated certainty about it that has us both concerned and excited for the future.

Concerned because certainly in the case of the BMW M5 and probably the Merc CLS 63 AMG, it's the end of an era. And excited, for in many ways the Audi RS 6 represents the guaranteed future of the super saloon beast as we've come to love it…

See, the BMW M5 is the ultimate in a long line of superb high-revving 100bhp-per-litre driver-oriented BMW M-cars that will sadly never be topped. In the name of a squeaky clean M-car future image, the next M5 will be a turbocharged V8 rather than a free-revving V10 masterpiece – and this car is as such already a classic.

The Merc CLS 63 AMG is likewise likely to make way for a turbocharged version of the existing 6.3-litre engine in the not too distant future, although AMG will be going back to its roots rather than plying new territory – the previous AMG 55s were after all supercharged…

And the Audi allegedly holds the key to the future through a turbocharged mill that brings with it ecological advantages. Apparently! We do feel however that Audi may have missed the point a little in this one – for while it shatters performance records, we found its real world fuel consumption (and obviously its emissions) to be considerably worse than the two aspirated cars it’s supposed to have a green advantage over. But more about that later…

So, this is an important one. We know the BMW and the Merc well, but what about this newfangled Audi with its direct-injection twin-turbo 5-litre V10 that’s supposed to be the new killer on the block…

Well, the RS 6 is the quickest car we have ever tested for sure, but to achieve that, it needed some special attention.

When RS 6 arrived at our offices on the first Monday of February, it was a hot and dry afternoon. Still, I headed out to the hills to feel it out and I took the VBox with to see if we could figure out how the test would pan out. I came back a tad disappointed – we battled to break a 6-second 0-100 although the overtaking times were, well… incredible.

Eventually using the old line-lock method of keeping the left foot on the brake and boosting it up on the throttle with the right before releasing the brake to launch, we managed a mid-five. But still that wasn't quite as good as the Merc or the Bee-Em in spite of that turbocharging and its apparent advantages at altitude – over and above the car's inbuilt power benefit.

But it was hot and dry and the car was warm by the time we got out there.

We later discussed this at length and decided to give the monster its best shot – we'd leave and head out to our test strip at sparrows in the normal ideal conditions, but make sure that the car was also in perfect fettle with under bonnet temperatures at the minimum, the intercooler as cool as possible and the air it was breathing also as ideal as we could get it…

Then it rained for the next two days and when Mario finally got a dry morning and gently headed out to the strip; and the conditions couldn't have been better. The first run was mesmerising – 4.3 seconds 0-100, a 12.4 second quarter-mile at 189km/h and wait for it – a 25.1 second standing kilometre at 246km/h!

But then we immediately ran it again through the 0-100 and it returned a 4.6 second 0-100, and again at 4.9 seconds and the fourth time with the fan now running, it was well back north of five seconds. That afternoon in 30-degree temperatures and after a short drive it was back to where we started – mid-five second 0-100s – and only if we line-locked it.

Incidentally, the car would only get into the fours using that method in ideal conditions and into the fives in the heat of the day. If it were a manual we’d be able to get the revs up to get it off the line, so we'll give it that best run, but remember, like the Lexus hybrid’s hot lap last year, the RS 6 had to be specially treated to achieve its quickest run…

The point however, is that the M5 and the CLS 63 will run in a band of 0.2 second figures whatever the conditions on the day or what was going on under the bonnet and unless you just drove your RS 6 out of your garage in the morning, it's likely that the oke in the M5 or the AMG 63 is going to bliksem you off the line…

He must however look sharp on the freeway – the fellow in the Merc or the Beemer – the RS 6 possesses the overtaking flexibility of nothing we have ever tested before – no matter what the under-bonnet conditions are a the time – so steer clear…

In conclusion of the Audi RS 6's in-line performance at Reef altitudes where most of them that will be sold in South Africa will end up, let it be known that in the correct ambient conditions and with the car working in the narrow envelope where it is happiest, this is the fastest car we have ever tested. And by some considerable margin.

But let either of those parameters slip and it’s all of a sudden a pretty average super saloon.

So, with that out of the way, let's continue…