Car and Driver does all the dirty work on this one.
Great read... http://www.caranddriver.com/comparisons/2014-audi-s5-vs-2014-bmw-435i-comparison-testWe figured the 4 would be indomitable in any comparo, but because we wanted to put its best foot forward, we lined up the baddest example available—a 435i with the $3100 M Sport package, which includes firmer dampers, springs, and anti-roll bars. The $1000 Dynamic Handling pack adds variable-ratio steering and adjustable dampers. With a 300-hp inline-six, the 435i starts at $46,925, but ours totaled $57,225 after $1900 in lighting upgrades, the $2200 Premium pack (satellite radio and keyless entry and start), and a few other nickels and dimes.
Audi’s aging S5, introduced for the 2008 model year, still represents the 435i’s greatest threat. It was born with a rumbling 4.2-liter V-8, but a transplant for 2013 traded two cylinders for a Roots-style supercharger. Its V-6 displaces just one cubic inch more than the 435i’s straight-six but makes 33 more horses and 25 more pound-feet, for totals of 333 and 325. Quattro routes the power to all four wheels, and $1100 of this example’s $59,220 asking price goes toward the sports differential that varies torque distribution between the rear wheels for sharper handling.