I guess I was in a fortunate position when I ordered my S5 SB that I had enough money to buy a fully loaded one, so I started with 'all boxes ticked' (except 'Audi exclusive' trim etc.) and then went through them and decided which ones I really didn't want to waste money on. So sunroof and tow bar got removed, and of course CD changer (why the f*** is that an option?), leaving me to agonise over if I wanted the TV option or not (in the end I decided against it because I can't see I'd need it and it is easily retrofittable). So anyway, I do of course have full ADS.
Phil, if you have not test driven cars with ADS options then you are in a difficult position to make a decision. However I'll try to give you an unbiased view. I'll start with two key questions.
1) Have you ever driven a car on different road conditions and wished that the ride was different? Now I don't mean driving a basic hire car and wishing it had firmer suspension, I mean driving a decent car and thinking 'this road is a bit bumpy, I wish the suspension was a bit softer', or 'this car is rolling a bit in the corners I wish the suspension was firmer'. If not then you probably won't benefit from damper control.
2) The same sort of question about pushing a car through corners. If you have never complained about understeering then you probably won't benefit from sports differential (I know that wasn't on your list but it probably should have been).
Now about each option:
ADS
As you probably know, if you choose damper control, dynamic steering and/or sports diff then you have to have ADS, but you can select ADS on its own. If so you can set engine/gearbox, steering (not dynamic), engine sound and ACC (if you have it) to your liking. Now I can't really prove it, but I believe that the setting for engine/gearbox does make the a difference beyond sport mode. I have tested my car in sports mode with ADS individual (engine/gearbox auto) against ADS dynamic mode and I truly believe that it is more responsive in the latter throughout the rev range. This alone should justify £220, but being able to adjust the other options too makes it even better.
Damper control
Drive a car with this and change the settings as you drive and the difference is obvious. Auto is close to what the 'stock' suspension feels like. In comfort the ride is indeed much more comfortable and even slightly wallowy. In dynamic it firms up and becomes almost harsh. Now for someone like me who wants to change to comfort over a rough road or have passengers who really prefer boring cars, but then when I'm on my own and want to have fun, stiffening up the suspension to improve handling, this option is great. But I can understand that for someone who doesn't want to faff about changing settings then the stock dampers are fine. But for £300 to get the choice and potentially a better handling car (in dynamic) then its worth it.
Sports differential
Even for £620 this is a fantastic bit of kit, if you use it. And of course that's why I asked the question above. I have seen comments like "only needed on a race track". I can only think that anyone who makes such a comment doesn't drive like me on twisty B roads (derestricted ones of course
). This is the one thing that challenges the criticisms that Audis understeer. This was a "must-have" to me and the main reason why I gave up looking for a used S5 and bought new.
Dynamic steering
This was the one option that I was worried about. I had test driven cars with and without it but couldn't really tell the difference on the test drives. Then another S4/S5 owner with it told me that he was annoyed by the 'sudden' changes in the steering ratio. Well now that I have it I am relieved that it doesn't annoy me, and in fact I find it rather subtle. Maybe Audi improved it in later models. I would love to know if the steering ratio in dynamic is the same as a car without it. If so I would definitely say that it is not worth £375. That's because in comfort mode I really do need to steer more than I want to, and the steering truly lacks feedback. In dynamic it is fine, and probably the same as a car without it. I guess until I can put my finger on a benefit of dynamic steering I'd have to not recommend it.