[MikeB]

Good question. I've done several front disc conversions but none at the rear. However, I know the main advantage discs have over drums is not stopping power per say, but standing up better to repeated heavy braking. But if your rear drums are in good working order, I doubt you'd notice any difference during everyday driving, unless you live in the mountains. Also having 12" or larger diameter rotors & calipers (which probably requires 16" or larger wheels) would probably increase stopping power over 11" drums. (Larger diameter results in more leverage when the pads clamp the rotor.)

But even if you get 20% more stopping power at the rear from a proper conversion, that's only 5%-10% more stopping power overall, because front brakes do most of the work.

For optimum drum brake stopping power, make sure 100% of the shoe surfaces are contacting the drums. With freshly turned drums and new shoes that's not going to happen because the arcs are different! And good luck finding a shop with a machine that can "arc in" new shoes. They are long gone with 10 cent Cokes. So that means you need new drums to go with new shoes for 100% contact. Also, make sure the rear brake hose is in good shape. If it shows any outward signs of aging, it may be expanding under pressure.