FifthGear has reviewed the 2012 BMW 640d M Sport, a car which the Bavarians claim, features the world’s sportiest diesel engine.
This engine is a straight 6-cylinder 3.0-litre unit equipped with three turbos which produces 313 HP and 464 lb-ft of torque. This means the 640d is even torquier than the 650i version and its V8 petrol, but despite its naughty exhaust note and the fact that its 0 to 62 mph sprint time is 5.5 seconds, FifthGear things that the diesel version 6 Series prefers to take things easier and cruise rather than be driven at high speeds.
Nevertheless the Brits still consider this 1.8 ton car impressive especially when taking into account that its combined economy figure is 51.4 mpg (UK rating), something that even the cheapest 1 Series will not be able to match.
The 2012 BMW 640d M Sport is priced from 62,000 GBP in the UK, which means it costs the same as the Mercedes SL and the Jaguar XK while being just as fast and twice as economical, so if you do want a GT that combines sportiness and refinement which is incredibly efficient, then Fifthgear thinks this version should be topping your list. 
2012 BMW 640d M Sport Review Video :

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Source: FifthGear via YouTube