I've upgraded my '73 Dart's stock discs 10.5"(?) to '73 C-body 11.75" and 1.25" thick rotors and C-body calipers.
Been screwing around a year with the wrong MC (1") where braking wasn't 'that' impressive', until I installed a 15/16" MC after which things got a lot better.
But I was still driving around with old brake pads. After I installed a set of Hawk HPS brake pads, the braking improved enough to my liking.

EDIT:
I have no back-to-back comparison between the old stock rotors and the larger/thicker C-body rotors.
The old brake system needed just about everything replaced and I rather install parts I already had on the shelf, and was an upgrade at the same time.