Here are my opinions comparing an Audi S5 4.2 liter V8 (not RS) and a newly purchased 2013 M3 Convertible:
I have had the Audi since mid 2010. It is my wife's DD and I have about 1/2 of the total miles on it. It presently has 40K. In my mind this car is the same as the RS as the HP numbers are so insignificantly different, they make no noticeable difference. The "newer" S5's have a smaller motor as to justify the premium price for the RS.
First thing is that comparing these 2 cars is not really "fair". The Audi is all wheel drive and to me that puts it in a different category. It's heavier, and by design has a huge unfair advantage against the M3 if it is to be used as a daily driver by someone who lives where the weather changes seasonally. If any one living where it snows is considering choosing between the two, for a daily driver, you choice is already made. ANY rear wheel drive car cannot compare with an all wheel drive car in this situation.
The Audi with a set of Blizzack's is unstoppable on slick roads. The only problem that comes into play is depth of snow as ground clearance is minimal.
Our car has the upgraded selectable "drive", I am not sure what Audi calls it. You can choose comfort, automatic, or dynamic. Depending on which you choose you would think you are in 3 different cars. I can't stand it in anything other than dynamic mode. I guess you can take the adjustments further, but who has time to figure that out?
For long trips, on the highway, I don't think anything out there can beat this car in stability and drivability. The car does not even come alive until 100 MPH.
It's quiet, stable, and very capable.
Fuel milage is so so, but does that really matter?
I do all my own maintenance on all my vehicles. The Audi is a breeze to change the oil. I thought the $9 a quart price tag was outrageous, until I heard BMW's was $14!
I don't care for the nav system, but then I don't like any auto's system that doesn't allow you to do something while driving.
The Bang & Olufsen stereo is one of the best I have ever listened too. Controls are typical European but relatively intuitive.
The car has plenty of power and more brakes than you will need on the street.
This being said it is no super car. If you want something with a faster 1/4 mile, buy something lighter.
At higher speeds, it seems like there is no end to the torque and power is always on reserve.
So I have a lot of experience with the Audi, and only 700 miles on the M3.
I don't put them in the same category as I said above, but I will say that the ride in the M3 is incredible. Rides like dream but the suspension behaves like a proper sports car!
I'll leave my opinion on the transmission reserved for now. I've been told "it gets better".
So far, I can't say much about the power. I have not yet "seasoned" the motor so I don't want to push my luck.
I do wish I would have looked at the numbers a little closer, prior. Over 400 BHP but less than 300 FP of torque? Did they take a lesson from the Jap bike makers?
The high rev motor does sound good, and it is unique. I don't care for the "drone" that some motor/exhaust combos make. It gets old quick.
The stereo is great sounding in the M3. Here I feel BMW has a slight edge. The controls (software) leaves a lot to be desired.
Probably the thing I like the best about the BMW is not present on the Audi. The little switch that "transforms" this coupe into a drop top. All the benefits of a convertible with out all the negatives. How can you beat it?
I don't see anytime soon where I will part with the S5. We just picked up an ordered Allroad for the wife to haul the dog due to how outstanding our experience with Audi has been.
I have driven a 2011 Mini Clubman S as my DD for the last 18 months and love it like no other car I have ever owned. Thus I have high expectations for the M3. But, in the end, I have a hard time putting the M3 and the S5 in the same category.