The reason I ask is that I want to change my E92 sport suspension to the BMW Performance Suspension (PS). I have read many posts from happy PS owners but I hesitate because my E92 is a daily driver that I commute 60 miles a day. A harsh suspension is not going to work for me, no matter how good the handling.
In a past vehicle I installed too stiff shocks. It was so bad after 2 days I took the truck back and told them to put in the old shocks. The indy shop told me that I only needed to change the rear shocks, because it is the rears (more than the front) that make a suspension feel 'harsh'. I followed the advice and it is right -- it is primarily the rear suspension that dictates 'harshness'.
If the E92 spring is 1" shorter than the E90, then it must be stiffer, otherwise the E92 would be bottoming out (less travel must mean stiffer or bottoming out). This means that if the PS rear springs are the same for both E90 and E92, then there would be more of a difference in how stiff the springs feel between the PS & E90 than for the PS & E92.