Well pal, here's the deal.
Like GTO put it, the E270 Cdi is faster than the E240. Case in point? Pick up this month's autocar, they gave the car an astounding 10/10. And yes, no merc has ever got that distinction from the boys at ACI. And if you are really worried about the racket that it creates, then i guess i suggest you to take a trip in its engine bay.... provided you fit in it.
. Jokes apart, once you start the car and the rpm gauge boils down to a constant idle speed, the noise would diminsh majorly and vanish once you are on the move. Typical Merc diesel traits.
Have a blast in it. Its so good, its worth waiting even if it has a 6 month waiting list.
Atleast I would.
Revv