Woah, old thread indeed! I've been running PSS on 21s since May, thank you X5M
I'm about to go back to 469Ms with winter rubber (and RFT). Different pressure front and rear is quite normal, in fact, a car that has the same pressures all around would be the outlier. I run 36/44 per the manual..I believe cars with a 3rd row are recommended to tweak that slightly.