To be honest I think your on the correct track and 20mm is possible I had 30 packs of 12mm laminate in mine yesterday at 18kg a pack and it sat a bit bogged down. Absolutley no issues with speed humps or the severely sharp threshold to my downhill driveway to which I’ve had a standard vectra bottom out.I think I can get away with 20mm, just.
Biggest win would be cancelling out the electronic damping!!! As you know yourself in sport mode or race it’s lethally harsh especially on motorways or national speed limit country roads. Both my mk4’s have had an essence of Christine about them in sport mode