My e39 Sport is on 17's but I've found over time that the recommended pressures on the door post are probably the Goldilocks setting. I've tried various adjustments, down and up, front and back but keep coming back to the recommended settings.

With newer BMW's some people run the tyres a little below recommended to try and offset the outer edge tyre wear but in 160-170k of e39 driving I've never had a problem with uneven wear on one that's been reasonably well aligned.

From memory I think that the recommended on 17's is 2.2bar/2.7bar (f/r)