We have 50K kilometres on our X1 xdrive 20d (2010). It is currently on second set of tyres (normal HP's). Pressure of 2.4 bar all round works very well
. Tyre wear is even all round, unlike the first set (run flats) done at 2.2 front and 2.6 back.
Tyre pressure definitely remains more constant with Nitrogen as a top up of pressure is needed once every 6 - 8 weeks.