Alas this is the trap that every comparison between the Audi brand and BWM brand fall in to, which is the quickest in a straight line and who's the quickest on a track. I agree on both counts the M3 will be the quicker car as it's design is several years newer than the RS4 but here's the problem, last time I looked I drove my car 99% of the time on the road.
Now as yet toll road aren't in the UK though I know other countries do have them, so the place over here that a new M3 will beat a RS4 over here is on a toll road, sorry wrong choice of words race track and the last time I when to work these type of toll roads aren't open. So in other works the RS4 will remain the king of the road or should I call it the King's highway.