It makes a strong case for choosing the I6 oil burner over the twin-turbo V8.

We spend a fair amount of time talking about the twin-turbo V8 version of the BMW 8 Series. Here in the UK the big grand tourer is available in M850i guise, which includes the force-fed 523-bhp 4.4-litre V8 and an eight-speed automatic with a manual shift mode. Buyers can also opt for the 840d which swaps the thirsty V8 for a 3.0-litre inline-six diesel festooned with a pair of turbos to make 315 bhp.

Why would anyone with the means to buy an 8 Series go for the diesel? It’s certainly not as quick as the 850 but there’s a veritable mountain of torque from the boosted six, enough to send the car to 62 mph in 4.9 seconds. That’s not slow by any stretch, and whether you choose petrol or diesel, you’ll max out at a factory-limited top speed of 155 mph. Also, the diesel is a whopping £25,000 cheaper.

Gallery: BMW 8 Series diesel on Autobahn

Watching this 840d top-speed video from Cars on Autobahn on YouTube makes the argument for the diesel even more convincing. The sprint takes place legally on an unrestricted section of German Autobahn, and if the onboard equipment is accurate, the 840d is a touch quicker than BMW’s published stats. Using launch control, this particular car hits the 62 mph (100 km/h) mark in 4.8 seconds, reaches 124 mph (200 km/h) in 20 seconds, and slips past the governed limit to reach a top speed of 160 mph (258 km/h). That’s the speed indicated by the car’s speedometer as well as a GPS readout on the windscreen, and it sure seems stable and surprisingly quiet while pounding down the highway.

We all love tyre-shredding horsepower, but seeing the big coupe gobbling miles in an effortless manner certainly offers us pause as to what version might be better as a daily-driven machine. But an 8 Series diesel could indeed be a tempting proposition.