Used Mercedes SL vs BMW 6 Series Convertible vs Porsche 911 Cabriolet

Hefty depreciation means big convertibles often make great used buys. But should you choose the luxury of a Mercedes, the prowess of a Porsche, or the all-round talents of a BMW?...

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Alex Robbins
18 Jun 2017 06:00 | Last updated: 14 Jun 2018 00:03

The Contenders

BMW 6 Series Convertible 640d M Sport

List price when new £72,630

Price today £26,000

Available from 2011-present

The soft-top 6 Series provides open air thrills for four, and this diesel-engined version can return almost 50mpg

Mercedes-Benz SL 350

List price when new £72,495

Price today £28,000

Available from 2012-present

The SL is more agile than ever, and a smart interior and folding metal roof add to the wow factor

Porsche 911 Cabriolet 3.4 Carrera

List price when new £79,947

Price today £58,000

Available from 2011-present

Sports car performance and dynamics turn every trip in the 911 into an adrenaline-fuelled adventure

Price today is based on a 2012 model with average mileage and full service history, correct at time of writing

Fancy taking in this summer’s sunshine in something with grace, pace and space to spare? Well then, we’ve got a treat for you. Three delightful used drop-tops all from the upper end of the market, all leather-lined and dripping with kit, and all promising the perfect blend of driving excitement and comfortable cruising manners.

What’s more, depreciation means you can usually buy cars like this for a fraction of their original price. Take the BMW 6 Series Convertible, for example. This version is still on sale today, almost unchanged, as a brand new model, but with a five-year-old example like the one we’re testing here costing a fraction of that price, you’d be mad not to consider it.

Used Mercedes SL vs BMW 6 Series Convertible vs Porsche 911 Cabriolet

The same goes for the Mercedes-Benz SL. Long has this two-seater been the drop-top of choice for celebrities the world over, and not without reason. The latest shape might be a little less elegant than those that came before, but it’s laden with equipment and has undeniable presence out on the road.

And if you’re after something with more of a sporting bent, there’s always the Porsche 911 Cabriolet. It’s a very different car to either of the other two, but no less practical or usable. And it comes with the promise of Porsche’s legendary chassis know-how, which should make it about as exciting a convertible as it’s possible to get. Time to find out which is best.

What are they like to drive?

Even this entry-level 3.5-litre V6 version of the SL gives spirited performance. From rest, initial pick-up is a little stately, but once the engine is at more than 3500rpm, the SL accelerates with far greater urgency. The engine is impressively quiet, too, and as revs rise it produces a sharp metallic exhaust rasp that’s very pleasing on the ears.

The seven-speed automatic gearbox is a bit old-school, preferring to slur rather than rush through the gears. You can counter this by selecting Sport mode and controlling shifts via the steering-wheel-mounted paddles, but if you’re too quick with downchanges, the gearbox simply refuses to play ball.

Used Mercedes SL vs BMW 6 Series Convertible vs Porsche 911 Cabriolet

The mechanical smoothness of BMW’s twin-turbocharged 3.0-litre engine is all the more impressive given that it runs on diesel. It comes close to matching the Mercedes in that regard, in fact, and it’s much more responsive thanks to the torque it produces from just 1500rpm. It hurls the 640d forward, revving quickly to its 5500rpm red line before the sweet-shifting eight-speed automatic gearbox grabs another gear.

Stick the 911 in fifth gear at 25mph and plant your right foot, and you’ll be doing 166mph before the engine runs into the rev limiter. That gives you some idea of just how strong and flexible the 911’s engine is. Rev it out in the lower gears and the 911 gains serious speed, seriously quickly.

Used Mercedes SL vs BMW 6 Series Convertible vs Porsche 911 Cabriolet

Of course, the 911’s real gift lies in its unstickable grip, beautifully judged suspension, strong brakes and sharp steering, which allow you to charge hard and kiss the apex of every bend.

The 6 Series Convertible is an extremely heavy car and its body flexes significantly whenever it hits any kind of bump. Vibrations rattle through the steering column, too. Even so, tight body control and strong grip mean that it can be hustled along twisty roads pretty hastily.

The SL is impressively eager to dart into corners and displays a composure that would shame many a nippy roadster half its size, and yet it’s a proper smoothie in town and on the motorway.

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Used Mercedes SL vs BMW 6 Series Convertible vs Porsche 911 Cabriolet