Why the comparison?
The 1 Series M Coupé is a car we've been desperate for BMW to make ever since we first heard about the 1 Series itself. Surely a small, light, relatively basic car with a huge engine shoehorned into it by BMW's M Division masters would be the best driver's BMW in decades?
Ditto the Cayman R, to an extent. There's a feeling that the Cayman is, by nature of its mid-engine setup, an inherently better balanced car than the rear-engine 911, and that Porsche has deliberately kept the power down so as not to step on its far more expensive car's iconic toes. The Cayman R is probably as quick and extreme as it's ever going to get.
How are they similar?
The BMW and Porsche have very similar performance stats for a start: 4.9 seconds to 62mph against five seconds, in the BMW's favour. And while the latter is a proper four-seater with a decent boot, neither is the sort of car likely to be bought on a whim.
For a start, the BMW costs £40,000, and nearer to £45,000 with a few options, while the stripped back Cayman is £52,000. A lot of dosh - especially for the BMW, which is derived from the company's cheapest model range. Both have six-cylinder engines, though the BMW's is twin turbocharged, and both send power to the rear wheels.
How do they differ?
In plenty of ways. We've touched on the practicality issue - the Cayman has two seats and two briefcases worth of luggage space - but there's a fundamental difference of approach here.
BMW has made its car as pure as any M model for years, by basically stuffing the chassis from the bigger M3 under a stretched out 1 Series Coupé body. The result isn't far off one of those Koolart cars - ridiculously beefy and exaggerated. But it's still designed for everyday use. The suspension, steering, brakes and 19-inch wheels are all from M3 stock, but there's none of the adaptive chassis trickery you get in most high performance cars these days.
Porsche, on the other hand, has pared back the Cayman S to make the R, taking out the air conditioning, stereo, door handles and, amusingly, even the cowl over the speedometer. The wheels are lighter, as is some of the body work (the door skins are aluminium) and there's a set of fixed carbon fibre bucket seats. Coupled to a 10bhp power hike, to 325bhp, the R is the quickest Cayman yet - and not too far away from a race car for the road.
The Cayman is wholly uncompromising. Don't like the height and angle of the seats? Tough. Want air conditioning? You'll have to ask for it. Want to open the door? Pull the little fabric loops where the door handles used to be. However, it all adds up to one of the most sensory driving experiences this side of a supercar. Every stone and crack in the road is felt and heard. The engine screams and roars behind your ears, the tyres rumble and the gear stick clanks through every precision rendered change. The steering blesses you with the precise ability to point the car exactly where you want it to go, at comical speed.
The BMW commands more respect. The twin-turbo six-cylinder engine seems to punch far harder even than the 4.9-second 0-62mph figure suggests. This is a seriously quick car. And while there's loads of grip and feel through the wheel, you're never more than an ill-informed throttle mash away from sending the back end outwards. Yet, mostly thanks to the traction control, it doesn't feel too edgy. And actually, it's so composed and well balanced that soon you'll be flowing from corner to corner almost as quickly as you would in the Cayman. It just takes more consideration.
So which one would we have?
The problem the Cayman has is basic comfort - lack of it. It's the one you'd choose every time for a hair raising blast on your favourite road, but the noise and constant vibration would do your head in pretty quickly if it were your only car.
The BMW has no such issue. While having eight tenths of the Cayman's feel and purity, it also has almost all the suppleness - and therefore comfort - of any other 1 Series. It's also the much quicker car most of the time. The stats don't lie: 369lb.ft from 1,500rpm plays 273lb.ft from 4,750rpm. Simply put, the BMW gives you its all from the get go, whereas the Porsche spools up to a bigger crescendo.
So, if it's one all encompassing performance car you're after, the BMW it is, but if you're lucky enough to have £50,000 going spare for a weekend toy, the Cayman is irresistible.