How much advantage in adding rear disk brakes?

I converted my Duster from 11x2.5" rear drums to 11.7" rear disks from @DoctorDiff ( I run 13" front disks from doctordiff as well). The most noticeable thing for me was that I have better braking control, I can brake harder without locking up the rears and the pedal feel is a lot more accurate than compared to drums. I couldn't say if the car stops significantly shorter, but I know that hard braking events feel a lot more controlled.

And yeah, the drum auto-adjuster thing sucks. They only adjust when you're backing up, and if you always back while turning the same direction (like if you back out of your driveway or into your garage the same way) then you can have one drum tighter than the other. The way I used to park my Challenger and my Duster at my house meant I was frequently turning the same way, and on more than one occasion during hard braking the rear wheel that would be on the outside of that turn would lock up first because it would adjust more frequently than the other side. Disks are always "adjusted" the same.

And DoctorDiff's 10.7" and 11.7" kits work with the OE style tapered adjusters.

Mopar muscle did a rear disk conversion on a '73 Dart Sport and checked the stopping distances between the rear drums and rear disks from 60-0. Their result was that from 60 mph factory disks up front and factory drums in the back the car took 133 feet, 6 inches to stop. After the rear disk conversion, the stoping distance improved to 122 feet 4 inches. It wasn't a super scientific way to test it, but it was better than most of the documentation out there. And the car involved was set up the same way as a lot of these cars, much larger rear wheels than fronts. The 80/20 thing is an estimate, it changes a lot based on how the car is set up- it's actual weight balance, the front to rear rake, the size of the rear tires. If you run much larger wheels out back than up front your balance may be a lot closer to 70/30.

The online article is a total mess now, probably something with being converted over or moved to Hot Rod when MM was bought out. The final distance used to be a caption on the second to last picture, but I don't see the captions popping up anymore. The hardcopy article is easier to follow, but that's the way it goes.

Rear Disc Brakes - All Bound Up - Mopar Muscle Magazine