Ridge,
We don't have any specific numbers off a dyno--yet. It is more of a seat of the pants feel that a number of us Scout Dieselers have noticed.
Our engines use an Airesearch turbo T-3 with an A/R ratio of 0.62--boost is limited to 6.5 lbs (bad things happen to this engine when going to higher boost pressures). The M/B 617 uses the same turbo with an A/R ratio of 0.48--boost at 11lbs. [Future installation planned with the 0.48 housing to reduce turbo lag while keeping the 6.5lb waste gate]
Without increasing the boost and no intercooler, the bigger exhaust helped out with mid-range and bottom-end torque. The big problem with the factory exhaust is the cast iron *elbow* to reroute turbo exhaust away from the starter. Mercedes exhaust flows smoother out from the turbo, but it is still not 3" in diameter.
Here are some links:
Diesel Scout forum
Diesel Scout 3" exhaust install
Elbow Eliminator--3" exhaust flange for turbo