I would assume it depends on what engine you have. small engines wont need as much front
Tyre pressures are a guide - personal preferece / time of year / temp all are factors. Clearly moving too far from oem spec is a risk but its worth playing around to see what suits your car. Mine is noticibly better with the higher front pressure on the road..
I'll have a look at mine as it does give pressures for 19 inch wheels.
It will probably be a bit different at the front as mine is a V6 TDI, but it should give you an idea and I will give you the 18" pressures so that you can compare with what is on your data label.