Not exactly. S5s are the mid-tier performance version of the A5 and are a little faster than the Stinger. RS5 is the top performer of the A5 line and is much faster than the Stinger.
A4 can be upgraded to S4, which is a little quicker than a Stinger, or (if rumors are true that it's coming to North America) the RS4 which is a lot faster than the Stinger.
Easiest way to remember is Audi's "A" designation cars are either a lot slower or a little slower than stock Stingers. Their "S" cars are typically a little faster.
A= You win
S= You lose/driver's race
RS= You lose
Close but not quite accurate. I agree the A5 is much slower and the RS5 is much quicker. However the S5 times are almost identical to the Stinger GT and its actually slower after 60mph.
2018 Audi S5:
C/D TEST RESULTS:
Zero to 60 mph: 4.3 sec
Zero to 100 mph: 10.9 sec
Zero to 140 mph: 25.4 sec
Rolling start, 5-60 mph: 5.6 sec
Top gear, 30-50 mph: 2.8 sec
Top gear, 50-70 mph: 3.5 sec
Standing ¼-mile: 12.9 sec @ 107 mph
Top speed (gov ltd, mfr's claim): 155 mph
2018 Stinger GT
C/D TEST RESULTS:
Zero to 60 mph: 4.4 sec
Zero to 100 mph: 10.6 sec
Zero to 140 mph: 22.4 sec
Rolling start, 5-60 mph: 5.0 sec
Top gear, 30-50 mph: 2.5 sec
Top gear, 50-70 mph: 3.2 sec
Standing ¼-mile: 12.9 sec @ 111 mph
Top speed (gov ltd, mfr's claim): 167 mph
If the race is from a dig the S5 will jump out ahead slightly, but then the Stinger will start gaining on it and will be walking away from the S5 by 70mph+ and definitely by the 1/4m(4 mph better traps speed). On a roll the Stinger should almost always have the advantage and will be quicker and quicker as speeds increase.