it will be an auto? (DCT, DSG)?
the 13 S5 is only offered in auto + 6 cylinder supercharged, correct?
Although yes it would NOT be a "fair" comparison S5 vs M3, but i totally understand where you are coming from.
I'm thinkin S4...might be better choice with 6MT if you want a quite unique sport sedan that doens't eat up crazy gas money on your 70 mile commute and still fun to drive on local roads and highways.
If you don't drive on track, I say BS to people who say "BMW drives so much better" when they actually drive 15 mile commute on 35mph~45mph speed limit roads.
And I live around where you live, I really wouldn't drive my M3 on that much commute on this local roads...S4 would be much better bet, although M3 will be a blast to drive on weekends on some nice mountain roads around here and tracks.
M3 is in fact better in value, unique, and as a sports car. 100 steps ahead of Audi S models.
Keep test driving and get what you need. Good Luck with your choice!