Audi released the A5 and its sport-tuned sibling, the S5, in 2007. The coupe showed remarkable styling and the S5 offered excellent performance. But now Audi ups the stakes with the RS5. Both S5 and RS5 use a 4.2-liter V-8, but the RS5 is tuned for 101 more horsepower, up to 450 over the S5. Audi also claims 22 mpg for the RS5, although that is not an EPA-tested number.