Its one of those things that can be affected by numerous factors.
As mentioned, the tyre profile will make a noticeable impact, especially with an s-line setup.
18" on s-line is fine with 235/40 etc but once you start going down to 35 then it can be felt.
That said, it's not always the case, I run 19" Oz alloys with 235/35 Goodyear eagles with no noticeable difference over running an 18" with a 40.
whether it's coil overs or a fixed height setup, the better the quality product the better the quality of ride will be.
Some will disagree with me on the next bit, which is understandable but the s-line setup on B7s is really less than ideal and when worn it's terrible.
It says it all when B7's are known for snapping rear springs on a regular basis because its rubbish kit.
I had both replaced at just over 30k miles because they had snapped, it's a common fault, I've never had any probs since going to aftermarket springs/dampers.
I was very sceptical about changing from the Bilstein b8's with H&R 45mm drop springs, which worked brill, then over to coilovers as I had heard so much negative press about them.
Poor ride, difficult to adjust, poor life span etc, all the things you expect to be good were being slated as rubbish, so I was in unknown territory to be honest.
From research it seemed to suggest that low-end coilovers were the main culprit for the negative feedback , owners that had fitted better spec and quality kit had no issues whatsoever, hence why i took a chance and went with the KW's.
I'm glad I did as I retained the excellent handling and user-friendly ride quality but also gained the ability to level up the front to back ride heights that are always off with the quattro's, nobody seems to have an answer why the fronts are too high and back too low or vice verser but its was nice to get that sorted out.
Maybe worth having a run out in a car that's got decent coilovers fitted to get a better idea on what they are like.
At the end of the day, w can only advise from personal experience and personal preference, the final choice is yours I'm afraid.