It is my expieriance the the back of the car is just as likely to cause the shaking as the front. If it is only shaking from 50-65 the worn out areas maay not even be measurable at rest. It is a harmonic problem if it only occures at specific points. I would also look at the rear trailing arm bushings and the rear pittmans. If the shaking is truly "violent" it's not likely caused by warped rotors. Warpred rotors would just push the pads away from the disc and if the calipers were stuck the brakes would be very hot even without and hard braking. Good Luck, John...