For those concerned about the sidewalls of GP4000/5000, the GP GT might be an option. I've used the 25s and they seem to ride as well as the 4000s. I may not be as discriminating as some but even I can tell they are nicer than Gatorskins. Relatively inexpensive.
https://www.chainreactioncycles.com/.../rp-prod109859 The 25s measure 28mm on 23mm (external) wheels.