These are the manufacturer's recommended pressures and one must experiment if one finds the ride unacceptable or the tyre wears unevenly.
Personally I have always found the recommended pressures have worked fine for me and my driving style. I also have the 20" wheels and have left the pressures at the recommended 2.3 bar, I don't see myself travelling at 100mph for any extended periods, if at all (officer!).
Tread wear appears even on what I presume are the original tyres, so time will tell. Hopefully an all season tyre will become available before they need replacing.