At the wheel of a model like this, you can see why Audi has in recent times achieved so much, so quickly. It's not perfect (the steering for example, could be sharper) but overall, let us try and define for you just why this car works as well as it does - starting with the engine. In the Cabriolet version, it's the same turbocharged 354PS 3.0-litre V6 TFSI unit used in the Audi S4, the difference being that in this open-topped model at least, you can enjoy the aural experience all the more, the eager crisp engine's snarling howl reverberating from buildings, bridges and trees every time you flick down a couple of cogs via the steering wheel-mounted paddle shifts. These shifters are standard in this Cabrio which uses an 8-speed Tiptronic automatic transmission. It ensures that you don't have to be an Audi test driver to replicate the quoted performance figures - rest to sixty in 5.1s in this soft-top model, on the way to an artificially limited top speed of 155mph.
Quattro four wheel drive is standard of course - a major advantage over BMW and Mercedes rivals - a system that today directs 60% of torque to the back wheels but, if conditions demand, can send up to 85% of power to the back or, if necessary, as much as 70% to the front.. You can also pay extra for the quattro Sport differential which sharpens cornering by speeding up the outside rear wheel relative to the inside one to help point the car into a bend. Adaptive damping's optional.
Audi has been careful to keep its sporting models both smart and subtle. So S5 buyers get just enough to differentiate their cars from humbler A5 models. The wheelarches house large 19-inch rims. These feature 'S5'-branded black brake callipers, one of the small differentiators that separate the profile aesthetics of the car from those of any ordinary 'S Line'-branded A5 cabriolet. Other unique touches include aluminium-effect door mirror housings, chrome trim on the door handles and, lower down, textured black sill trim tops.
Inside, the three-spoke sports steering wheel is bespoke. And another unique touch lies with the brilliant 'S' Super Sport nappa leather-trimmed seats that feature a lovely quilted finish and pronounced side bolsters. Otherwise, apart from lovely alcantara trimming on the doors and a few elements of S-branding, the ambience is exactly as it would be in any plushly-specified A5 Cabriolet model.
The acoustic fabric soft top fits as perfectly as you would expect and can be operated with a useful one-touch opening function (why has no one done that before?). Here, a flick of the switch is all it takes to open the soft top fully automatically in 15 seconds or close it in 18 seconds at speeds of up to 31mph. When the top is down, bootspace reduces by 60-litres. When it's up, you get the same 380-litre capacity that the previous generation model could offer.
You'll need a budget of around £52,000 for a Cabriolet S5, though you can save around £5,000 on that by going for the Coupe or Sportback versions of this model.
On to the S5 value proposition in comparison to rival brands. We'd say that the Cabriolet version of the Mercedes-AMG C43 4MATIC is the most direct rival to this car as it's the only precisely-matched competitor that also offers 4WD. The Mercedes is just as fast as this Audi, fractionally more powerful, a touch more expensive but, perhaps most significantly, will cost you about 10% more to run.
Otherwise, you're looking at rear wheel drive alternatives - probably something like the Convertible version of BMW's 440i M Sport, a model that's fractionally cheaper and a car that all the magazines will tell you is better driver's choice. We wouldn't argue with that but we'd also point out that the BMW is around 30PS down on this Audi, so takes nearly half a second longer to get from rest to 62mph - at least in the dry. In the wet, quite frankly, a 440i driver wouldn't see which way this S5 went.
You might think that the turbocharged V6 in this Audi is no eco-warrior - expect 36.2mpg on the combined cycle fuel and CO2 emissions of 177g/km of CO2. Insurance is predictably expensive at group 42E. What else? What about maintenance? Service intervals will vary between 9,000 and 19,000 miles, depending on how hard you drive the car; somewhere in that span, the need for an impending garage visit will flash up in the instrument binnacle. In fact, this car can even book its own service appointments via an 'Audi connect safety and service' system app.
On to the warranty. All contenders in this class get three years of cover but whereas you won't get your mileage limited in this period if you opt for something made by BMW or Mercedes, Audi rather meanly restricts you to 60,000 miles. Optional extra-cost warranty packages can extend the cover to either four years and 75,000 miles or five years and 90,000 miles. If the worst happens and the car breaks down, there's free roadside assistance included for the first 36 months of ownership.
You could drive an S5 Cabriolet for the whole of its motoring life without suspecting the beast that lies beneath its bodywork. Some owners will - and that's a pity for this Audi's split personality can also promise a remarkably agile driver's car.
True, it isn't quite as track-focused as a BMW M4 Convertible, but then, it isn't as expensive to buy or to run either. As an ownership proposition, it's quite simply a more complete choice that sounds great, looks brilliant and is quite beautifully engineered. Audi's S badge always delivered a special experience. Now it's a properly sporting one too.