I recently switched from a 2011 TTS, which has the same 2.0 litre turbo engine as the S3 ....
To a 2013 supercharged 3.0 litre S5, so same engine as the S4 ....
Absolutely no looking back at all and HUGE step up in - pretty much every department other than than handling perhaps as its a bigger heavier car.
But ....
engine is amazing, no lag, just instant power and masses of it.
Quality is a massive step up and all materials feel very 'premium'
Even the leather used feels softer and thicker.
Seats are to die for - in terms of looks and comfort.
6 cylinder is so smooth - no more 4 pot rattles at idle or on start up in the morning.
Added luxuries at no extra cost like the cruise, auto lights wipers, leccy seats, extended leather, DAB, B&O, privacy glass etc.
S-tronic suits the car so much and this is my 1st after being manual all the way.
Effortless cruising in calm silent comfortable cabin .... with power when you want it, did I mention that
Wonderful exterior looks and front & rear lights are amazing.
Solid thump when you close the doors.
Just feels a BIG step up from the TTS and as I did not rag the TTS round country roads I was not so bothered about losing a degree of agility and admit to enjoy straight line speed more and acceleration so the S5 is perfect.
I wanted something with useable rear seats and which would take me on long journeys and eat up motorway miles when called for as the TTS was pretty hard in terms of suspension and was ok on motorways and wind noise was noticeable.
The S5 is a wonderful car to own and drive and I am sure the S4 will be too, sharing many of the same components.