The US version of the 540 varies power assist based on engine speed, which is a pretty dumb algorithm. What you want is servotronic steering, which varies the boost based on the speed the car is going, giving perfect road feel from parking lot to autobahn. For some reason, BMW does not allow the US 540 to choose this, but it is standard on the M5. This would be a great project for someone to document the parts and procedure for adding this feature to existing 5 series.