I have had disc brakes at both ends of two different trucks, both over 1 ton rating, and the calipers and rotor size was the same front to rear.
Both trucks stop very well, and even with a load have no problems stopping quickly.

On another note, I had a 95 VW Jetta, all disc brakes. Traded it for a 98, and the newer car has drums in the rear, I figure that is a step back wards.

Grigg

•1951 GMC 250 in the Project Journals
•1948 Chevrolet 6400 - Detroit Diesel 4-53T - Roadranger 10 speed overdrive - 4 wheel disc brakes
•1952 Chevrolet 3800 pickup
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"First, get a clear notion of what you desire to accomplish, and then in all probability you will succeed in doing it..." -Henry Maudslay-