After talking to my local tyre dealer I have raised the pressure about 0.3 kg above the recommended, i.e. anout the same as full load.
Car handles better, consumption goes down, tyre wear is symmetrical but the ride gets more stiff. On a previous car I raised it even more and consumption was even lower.
I think the X3 is so heavy that it will suffer from high speed cornering, it is a SUV not a sports car