As far as a less-restrictive exhaust goes, I would imagine the setup on a Benz diesel is pretty much optimized in its stock form.

Having said that, I've heard more than once that you can't have too large an exhaust on a turbocharged engine. That's why many aftermarket companies sell absolutely HUGE (4 in. and larger) exhausts for turbodiesel pickups. However, the guys driving these pickups are turning up the boost and fuel delivery substantially beyond factory settings. A stock Benz diesel probably wouldn't benefit much from an uncorked exhaust.

It's interesting to note, though, that semi-tractors with single turbochargers often have massive dual air filters and dual exhausts. However, a 120 hp, 3 liter Mercedes-Benz diesel is not a 550 (or more) hp, 14 liter Caterpillar.

Aaron