Buying used: Porsche Boxster vs Mercedes-Benz SLK

Buying used: Porsche Boxster vs Mercedes-Benz SLK
Buying used: Porsche Boxster vs Mercedes-Benz SLK

What’s the best second-hand buy for £30k: six-cylinder Boxster S or V8 SLK55?

Depreciation can be a great thing, especially when you’re talking about buying a high-value sports cars second-hand. Within five years, some models can shed around half of their new value without losing any desirability. Two such drop-tops are the old-school six-cylinder Porsche Boxster S and the V8-powered Mercedes-Benz SLK55 AMG – so here we’ve put them head-to-head.

The SLK55 AMG range-topper can now be had for less than £30,000 – £25,000 below its new price. Meanwhile, all pre-2016 Boxsters have the great-sounding six-cylinder engine, so while they’re cheaper now, their collectability status for nostalgic Porsche enthusiasts can’t be denied.

The 416bhp 5.5-litre Merc V8 beats the 3.4-litre flat-six Porsche by 105bhp, but with its steel drop-top it’s 300kg heavier, which means there’s little to choose between the two on a fast, straight road. While the thunderous SLK55 musters more muscle at lower revs, fighting for traction as it does so, the fabric-roofed Boxster screams up to 7000rpm-plus.

A lower kerbweight means the Porsche can stop on a sixpence, yet you’ll barely touch the brakes through a series of fast bends, as the Boxster handles brilliantly, stays flat and exhibits superb composure. Its decently weighted steering is accurate but not outright sharp.

Meanwhile, the SLK’s weight makes it less willing to change direction, even if its steering is quicker and more communicative. It has to be physically hustled through a series of bends. Its sluggishly responding seven-speed semi-auto doesn’t help, while manual control via the steering-wheel paddles isn’t as instant as it could be. We prefer the Boxster’s joyful six-speed manual, and this is also preferable to Porsche’s seven-speed semi-automatic PDK option, which can sometimes get slightly confused.

Our test car’s optional adaptive suspension ‘de-firms’ the standard ride and delivers a smooth drive in Normal mode, especially at high speeds. It’s in contrast to the Merc’s standard set-up, which can crash over potholes and jostle the occupants when cruising.

Converting to top-down mode takes 20 seconds in the SLK and only when stationary, and nine seconds in the Boxster at up to 30mph. The latter’s passengers are better protected from the wind with the optional wind deflector, which comes as standard in the Merc. Our car also had the optional Airguard system, but we didn’t notice it had much effect. Roof up, the Merc is more refined, whereas its rival suffers from road and engine noise when cruising.

At least the Porsche boasts nicer-feeling materials and switchgear plus a more adjustable driving position and better kit levels. It all looks more sophisticated than the SLK’s trim – which is a surprise considering the Merc cost nearly £10k more when new – although the latter has a leather dashboard and attractive heater vents.

Another shock is that the SLK officially returns 33.6mpg against the Boxster’s 32.1mpg, despite its engine being two litres larger. The resultant lower CO2 emissions pay dividends in business car tax and VED, too. The Merc is also cheaper to service, and although its initial depreciation is huge, things eventually flatten out and it ‘catches up’ with the Porsche. When it comes to running costs, a model of this age has a distinct advantage over the Porsche, but even that car is not hideously expensive to own.


We love the Mercedes-Benz SLK55 AMG’s noise, theatre and straight-line performance, but its uninspiring ride and uncomfortable handling let down this sporting car – as does the dim-witted transmission. Its cheaper running costs can’t make up for this. On the other hand, the Porsche Boxster S has a superb chassis, strong performance and classy, sporting cabin which make it strongly recommendable for anyone looking to buy a proper sports car on driving and ownership experience rather than simply price.

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