The Wisefab BMW E90 E91 E92 Rear Suspension Arm/Hub Knuckle Kit, offers the completely revised kinematics and roll centre for ultimate grip / traction, along with dual rear caliper mounts so you can us a completely independent hydraulic handbrake .
As you can probably tell from the images, this kit is a bit of a work of art! , and I think it's fair to say that if you are using an E9X chassis in competition, this is one of the best alterations you can make.
Please note: This kit is not currently 'direct bolt on' with cars using an E9x M3 rear subframe. The toe arms would need shortening by approximately 15mm to use on an M3 subframe, or alternatively you can fit a non M3 subframe to the M3.