Right, so to double check you are looking at a standard Gen 2 GTS which is -20mm and another Gen 2 GTS that has the optional -10mm instead? Presume both are Coupe as standard on a GTS Convertible and Targa are -10mm.
I laboured over this one and went for the standard -20mm and also Axle lift. I was very worried about the ride as after ordering I realised I had messed up as I had tried a Convertible with 'standard' GTS PASM (so -10mm) and had therefore gone for standard on a Coupe, but that is -20mm. That was based on driving a Coupe and the Convertible GTS back to back to decide about the gearbox (Man Vs PDK). I felt the Convertible rode massively better, but put that down to it being run in whereas the Coupe was brand new. I was also put off the Coupe by the manual. After 3 years with PDK the positioning of the clutch and gearstick felt really weird to me. Plus I soon tired of the Auto blip, but I digress!
So I went for standard -20mm in some ways by mistake. The car is firm, but not choppy. It is stiff, but not crashy. I do tend to run the tyres in Comfort setting and even then usually knock an extra 1 or 2 PSI off all round as well. So TPM always says they are fractionally low. But it is fine. The car has a really nice gait and flows very nicely. I prefer it to my Gen 1 C4s which was -10mm as that 'floated' a bit. I've also got RWS so that may factor in. No PDCC.
There are speed humps near me and TBH I often forget to use the axle lift and have never had an issue with -20mm. Given the C4 GTS clears then I think my old C4s could have probably gone over them quicker, but I always slow anyway so no issue really.
There is a steep access ramp at work and if I go down that at anything more than a crawl it rubs the plastic strips where the C4S just cleared it. If I use Axle lift for that then it is absolutely fine.
Cant help with -10mm, but here is -20mm!
Apologies for the waffle. Not really what you asked, but it was a big deal to me post ordering as I was worried -20mm would spoil the car for me. Not a bit of it.