This is good to know. I actually asked this question some time ago because one of my family members accidentally drove in S4 down the freeway for a little bit. Seeing this discussion about S mode simply prompted me to ask again, as I'm a little paranoid about this sort of thing. Again, thanks for the input.

 

The rev limiter for each gear should protect the engine. Unless you have the radio or other entertainment up loud, you should hear the engine straining as it approaches redline for that particular gear. staying at the redline for a prolonged period of time could potentially cause damage. The fuel cutout will cause the engine to jerk once max engine speed is exceeded. You should feel that jerking. If the engine does not jerk, it is probably operating below the redline, but much faster than normal. Excessive fuel consumption will be the worse thing that can occur on a normal broken-in engine in that scenario.

Watch your instruments occasionally and you should be able to see when the revs are high. It will take a bit of effort because the car is so smooth.

Take care!