If the additional 45kg added to the Mazda’s weight by a metal roof raised eyebrows, the Merc’s 350kg handicap over its Japanese rival calls for Botox injections. However, the SLK is 23bhp and 51lb ft to the good versus the naturally aspirated, 158bhp MX-5 RF, and is both quicker to 62mph (7.0sec against 7.4sec) and more frugal (43.5mpg beats 40.9mpg).
Inside, the SLK is unsurprisingly ritzier. Soft-touch and satin-effect surfaces abound, complementing the leather upholstery and solid, precise switchgear. Ergonomics are equally hard to fault, with firm, enveloping seats that can be set low enough to leave sufficient cranial clearance for a tall driver when the roof is up. A boot divider must be in place before the SLK’s lid can be lowered. It slashes the load capacity from 335 litres to 225, but either configuration easily trumps the MX-5’s meagre 127.
Efforts to suppress cost and weight define the Mazda’s cabin. The stripped-back feel suits the car’s intentions, but you can’t ignore the shortfalls in tactility, adjustability and robustness compared to the SLK. Its seats match the Merc’s for support, but minimal vertical adjustment leaves me a little high, with bonce brushing roof. The steering wheel won’t adjust for reach, there’s no glovebox and the centre console’s infotainment dials are sited too far back to be easy to reach.
However, this being Sport Nav trim, the Mazda gets welcome toys that are missing from the Mercedes, including a responsive 7.0in touchscreen with sat-nav (the SLK’s 5.8in screen is inert and nav-less), rain, dusk and rear parking sensors and heating for its leather seats to broil your behouchie during chilly al fresco sorties.
Firstly, we race the cars without turning a wheel. The Mazda’s elaborate up-and-under folding routine takes the spoils in our top-dropping competition, its roof collapsing in 15sec compared with the more straightforward Mercedes’ 20sec. Neither one requires manual intervention.
Igniting the MX-5’s engine brings a subtle vibration to the cabin. The unit sounds bland when you pull away, but there’s steadfast urge from 1500rpm, and once you’re exploring the purple patch between 3000rpm and the red line’s 6500rpm there is vibrant throttle response, a decent amount of shove and a loud but racy soundtrack goading you on. More enjoyable still is the short-throw six-speed manual gearbox, whose gratifying mechanical action survives the most aggressive of shifts without flinching.
The SLK’s sports exhaust, which came as standard with our test car’s AMG Sport trim, emits some droning during low-speed operations, then a gruff chunter with turbocharged overtones ensues. It becomes quite noisy with revs, but delivers neither the brashness nor the character of the Mazda. Anything from 2000rpm lends the Mercedes strong progress and there’s little in the way of turbo lag, although acceleration wanes a bit at 6000rpm.