What is it?
According to Bentley itself, the key differentiator between the two models is this: the Mulsanne is a car most of its owners buy to be driven in; the Speed, on the other hand, will be bought by customers who want to do the driving themselves.
Hence the reason it has been massaged in all sorts of different directions to be a good 15 per cent more responsive for whoever is lucky enough to climb behind the wheel.
Of the 1100 or so Mulsannes that Bentley will make and sell over the next 12 months, approximately 300 will be the more expensive, more sporting, £252,000 Speed model.
Interestingly, Bentley also expects the vast majority of Speed sales to occur in Europe and the USA, not in China. This is despite that fact that the Far East has been the biggest single market for the Mulsanne for the past few years.
So what do your get for your additional £25,000 beyond the price of the regular Mulsanne? The biggest changes occur beneath the bonnet, where the twin-turbocharged 6.75-litre V8 engine lies.
This leviathan of a motor has been thoroughly revised at the top end to produce and extra 25bhp, making 530bhp in total. Which doesn't sound all that significant until you realise what's happened to the torque peak, and to the way the torque is delivered.
Maximum pulling power has risen from 752lb ft to a vaguely terrifying 811lb ft – but of arguably more significance is the fact that this peak figure now registers at just 1750rpm, and it stays pretty much flat between there and 4200rpm. The previous engine's peak figure wasn't attained until 2250rpm, and in that case it really was a peak.
In reality, then, the Speed should feel much torquier and, therefore, be much faster than the Mulsanne, hence the reason why Bentley now quotes some fairly hair-raising acceleration figures for the car. Zero to 60mph takes a mere 4.8sec, zero to 100mph 11.1sec, and the top speed is a deliciously irrelevant 190mph. This has enabled Bentley to claim that the Mulsanne Speed is 'The fastest luxury saloon in the world.'
Quite what owners of a Mercedes S63 AMG would make of such a claim isn't clear but, either way, the Speed is an indecently rapid machine considering it mauls the scales at a fulsome 2685kg.
Not only is the engine more potent but, as is the requirement nowadays from all cars, from all creeds, it's also cleaner and more efficient than before. Emissions and economy have both been improved by around 13 per cent. In the real world Bentley claims the Speed is 2-3mpg less thirsty than a regular Mulsanne.
Elsewhere, the air suspension has been recalibrated to deliver more sporting responses when Sport mode is selected within the new Drive program. The same goes for the steering, the eight-speed ZF gearbox and the throttle mapping: each of these can be set to whatever individual mode a driver might want by selecting the Custom function.