In my previous e60's, I've used both the Eibach options.

Firstly, I went for the ProKit...the drop was quite subtle and retained the comfort, as didn't want to lose that.

I fitted the Eibach Sportlines to my last e60, the drop was a bit more and I didn't find much difference in comfort, compared to the ProKit.

If chosing one option again, I'd go with the Sportlines, just that extra drop gave the car that more aggressive stance, without being too low or losing your comfort.