In my opinion, more people go from stoplights than from a highway roll, but is this in any way relevant?
From my point of view, here's how it tends to stack up, performance wise:
Drag Strip - Minor advantage to the RS5, given its AWD banzai launch. Best M3 magazine time I've seen is the C & D 12.4 @ 114 in an auto. Best RS5 time is a 12.2 @ 113.6 from Road & Track.
Out on the highway, side by side, it seems as if the M3 has a minor advantage, given its slightly better power to weight ratio, and the Audi's AWD paraphernalia. I'd guess that from, say 120 and up, the Audi's horsepower advantage would tend to assert itself, resulting in a slight advantage at that point. On the other hand, there aren't many races in the U.S. from 120 up. In point of fact there were seven such races in 2012, and two so far in 2013.
Race track: Advantage Audi, by a fairly small but measureable margin.
Back road: Perhaps a slightly larger advantage to Audi, based on the fact that everybody's a bit more timorous in this environment, and the Audi is easier to just punch it out of corners.
Back road, continued: On the other hand, unless you're in a battle to the death with your buddy in the "other" car (in which case you're both idiots), the bimmer is the back-road bandit of choice, with more nuanced steering, and that ability to go from understeer to neutral to oversteer that only rear wheel drive cars can achieve, given some expertise behind the wheel.
Yeah, the Audi is very good for an awd car, but the bimmer is the better "sport" driver by a clear margin.
So, what does this come down to?
Nothing. These cars are remarkably competitive, so pick your poison.
PS - Both cars sing the 8000-rpm song so beloved of M devotees on this forum, so nothing to pick from there, although I think the Audi sounds more delicious in everyday driving.