Speedy, the Crossfire's peak torque is reached at 3000 RPM's, this also seems to be the RPM range where many drivers have discovered their best MPG readings.
I assume that is because the engine is neither laboring, or over extending its capabilities.
The Crossfire will run at 2200 RPM's at highway speeds staying with traffic all day long. But by doing so (even though you wouldn't realize it) you're actually putting more stress on the engine by "lugging" or "taxing" the engine. Simply because it's not operating in its most efficient power zone.
3000 RPM's is exactly 1/2 of the engines redline. I would imagine a "stock" Mercedes engine could probably run continuously (at 3k RPM's) on a dyno, with nothing but fresh oil and fuel, at proper running temp for a 1/2 million miles with very little maintenance, besides some new spark plugs, and coils. Just my opinion.