The RS5 Cabriolet is the drop-top version of Audi’s BMW M3 rival, and arrives nearly three years after its closed-shell sibling. Deliveries start in April 2013, and it costs from £68,960.

The most notable highlight over an RS5 coupe is the roof. Audi once again eschews the fashionable but heavy hard-top, opting for a three-layered, electrically folding fabric hood that opens in 15sec and closes in 17sec, at speeds below 31mph.

At the RS5 Cabriolet’s heart is the same naturally aspirated, high-revving 4.2-litre V8 engine as the RS5 coupe and RS4 Avant – no turbocharging here. Power is metered out via Audi’s quattro all-wheel-drive, with a crown-gear centre differential and torque vectoring.

Audi’s sport differential – which continually varies the torque spread between the rear wheels to benefit agility – is standard equipment, as are the firm’s new weight-saving ‘wavy’ brake discs (now an RS staple) with a ceramic set-up a pricey option.

It’s fair to say the RS5 coupe hasn’t lit our fire so far. On first impressions, though, this new car feels better, the RS5 Cabriolet displaying dynamic changes that have also been made to the facelifted coupe. The bad news is that electromechanical power steering replaces the old hydraulic rack; it’s quick and keen enough, there’s just no natural feel, and it reveals too little about the state of front-end grip.

Better news comes in the shape of software tweaks, from the dampers to the Drive Select modes, also exhibited on the latest RS4 Avant. The RS5 feels more natural and composed than before, and follows your inputs more precisely. It’s still very much a fast Audi – quattro all-wheel-drive making it easy to drive unfeasibly fast (often in less than ideal conditions) but harder to engage with. But its engine sounds simply wonderful (especially with the optional sports exhaust) and has a bigger swell of torque than an M3’s. It’s easy to end up short-shifting through its seven-speed S-tronic gearbox, when the biggest fireworks – and the most sonorous noises – live north of 8000rpm. It sounds especially good roof down, of course. Weighing a not inconsiderable 205kg more than the coupe, though (topping 1930kg), the RS5 Cabriolet inevitably feels heavy under braking and when subjected to repeat direction changes.

The ride remains firm but doesn't seem as unsettled as pre-facelift coupes, while the scuttle shake that afflicted the old RS4 Cabriolet appears all but absent; the caveat is that the press launch was held on France’s Col de Vence, a fantastic road that’s smoother than British tarmac and on which a V8-powered convertible will nigh on always thrill. Full judgement will wait for when we try the car in the UK, but this first taste bodes the RS5 drop-top well.

Its most direct rival is the BMW M3 Convertible. Over £7000 cheaper but 30bhp shy of the RS5, it’s a car that will soon be retired. It’s rear-wheel drive compared to the quattro-driven Audi and gets a folding metal roof rather than the RS5’s soft-top. It’s more fun to drive, but its limits are less accessible than the Audi’s.

Whereas Audi’s RS models used to be known for exclusivity, with just one model rolling off the production line at a time, the range is now ever-increasing. By the end of 2013 there’ll be eight Audi RSs available, with an overall annual sales target of 15,000.