did you get a copy of the wheel alignment print out?
i watch the workshop did my suspension transplant and pretty much learn what it takes to assemble suspension. If i read your post, the drop in your ride with the breyton springs is quite accessive given you kept the existing shock. For your info, the original sport suspension for normal e60 and that of M5 gave you two fingers gap (asian man fingers those are) on driver side and 3 fingers on left hand side. 15mm difference to standard suspension. Of course the M5 design and set up are altogether different but there are reasons for not bringing it down any lower i suspect.
BTW, do come to the sunday meet up and get more info there from fellow e60 owners!
cheers