I generally drive an S5 almost each day. No one has mentioned torque! HP is only part of the equation. The S5 is hands down faster the the Z with more then double the torque. Our cars are great for the price point!! Bang for the buck!
We don't have Quattro, Servotronic steering, Lane Assit, Parktronic, Self leveling Bi-Xenons, Bang & Olufsen, MMI, LED DRL, Nappa leather, Infotainment, Battery energy management, Electro-mechanical parking brake, Voice Control, etc, etc...different beast!
Also if you can't afford to own a German or Italian high end vehicle, which is indeed costly to up keep, then stay away!
I have a ton of customers that can and do! This allows me to own my 370Z!!
Audi's are awesome to drive at their limits! They make bad drivers look good! It takes a ton of control modules, heavy engineered powertrain, and tank like structure to give the driver that confidence. Of course these things need to be maintained!! $$
These vehicles shouldn't be compared!