The front end on my car is really - really stiff that's why I stiffen the rear to reduce suspension travel which reduces the camber angle change and it works: the car starts to slide easily on the rear and thats what I like not to fight with the understeer if I really hummer it otherwise it is insanely stable and fast on corners and bends...
Rear diff poly bush mount really makes that a difference? I have only puted the Powerflex kit to the beam ends...