Chris, I was told by the guys at Eurocharged that it depends on the tranny, Stick shift vrs auto. However the revelimiter on my six speed was set factory at 5740 RPM. This to allow for over spinning under heavy acceleration.
I think the autos are set at 5800.

Mine is now set gears one, two three at 6300. I am almost never there holding at 6000.
Gears four, five, and six, are set at 5800 RPM's

These engines are good to 6800 easy. The worst you should get at those RPM's is valve float, which should do nothing as it isn't an interference engine.

Of course, I have had an unexplained issue which could be related to high RPM's. However I have had several V6 engines, non Mercedes, that regularly hovered around 7,000 RPMs and had no problems.

Just my two cents.