I'll say now that I'm a fan of the super-estate class.

Having spent a few days in an M5 Touring, I can honestly say that I would love to indulge in a 500bhp estate if I had the need for a comfortable family run around, and the money to fuel a car returning 16mpg.

That's because I'm a self confessed performance-car addict, and would nearly always choose the fastest or best handling model available in any range if money were no issue.

But that's not reality. Reality is that the M5 Touring costs £66k, and a 535d Touring costs £20,000 less.

The new Audi RS6 Avant has brings this into focus. It has a 5.0-litre, twin-turbo V10 putting out 572bhp. Remove the limiter and you'll see 200mph in an estate.

But who would buy a £77,000 RS6, when you can get a 3.0 TDI A6 Avant for £40,000 less? The big diesel A6 isn’t a performance car by any stretch of the imagination, but it's still quick, refined and will do double the mpg. More importantly, you could buy a used Noble M12 GTO with the remaining cash and still have enough left for a new conservatory.

As ever with this kind of car, it's a case of how much money the buyer has to burn, and where the priorities lay. Whatever the reasons, the RS6 Avant will sell.

Even so – do these cars really make sense, or are they a step too far?