Le Chef

The S5 is not an M3 competitor - more a 335i competitor. The V8 is on the way out - less than a year to go before it's replaced by the V6 with supercharger currently going into the S5 Cab and S4 Sedan. That engine is almost a teetotaler by comparison.

The V8 sounds amazing - woofly and refined - but it doesn't pull that hard. The RS4/R8 version of the V8 would be a great shoe-in but Audi seem to have other plans for the RS5.

useridchallenged

No one has mentioned tires in this thread, but I find the Michelin PS2 to be noticeably quieter than other tires (and they stick pretty well for a street tire, are predictable, and wear well, too).

The 996 is quieter than the 997, so I'd throw that out as an alternative. The 1999 and 2000 996 is a bit noisier than the 2001-2004, but still quieter than the 997.

Alas, the 996 is a bit more civilized than the 997 in its performance, but I'd still take the 996 over an M3.

So I'd recommend a later model 996 with Michelin PS2 tires. Don't know if 17- or 18-inch tires are quieter than 19-inch tires.