I can't put a confidence number on the 50% figure. You'd have to poll the true aero experts like J Cobb, A Coggen, R Chung, Chicanery, or Tom A for a better estimate.
Don't overlook the handling consequences of a 90/90 combo. It's been said, and I've even bought into it myself that a rear disk moves the center of lateral pressure rearwards and improves handling. I don't quite buy that any longer. Yes, it does move the CLP rearwards, but it also increases the magnitude of the lateral force by an offsetting amount. Further, the rear disk's location in the frame gives it no effect on steerer tube torque. Nevertheless, it does have a gyroscopic stabilizing effect due to its higher moment of inertia. It's this higher MI that I believe is really behind the improved crosswind handling of a rear disk.
"100% of the people who confuse correlation and causation end up dying."