If you are happier with a less firm ride and high walled tyres, why not choose a GT spec with some options rather than buying the one with the sports suspension and big wheels?
I can see why you think it might be harsh, but I've been surprised at how not harsh it is at all - even with our sh*t roads.
I testdrove a GTD without DCC and 19's and have a GTD with 18's and DCC - the test drive was quite nasty, I don't think I could have lived with that, but probably would have got used to it.
Normal mode for DCC is just fine, when the potholes get big or just on a long old motorway haul whack it into comfort and enjoy the luxury. Sport is ok, you do feel the difference - whether you want to feel it is another matter

It actually what I like best about my GTD - it can be all sorts of different cars depending on which buttons I push (not just DCC) and how much I hoof the gas.
Only thing I'd love to change is the road noise, but thats those crappy tyres and soon they will be gone!