Power assist with disc brakes will cut your leg effort in half. It won't make it stop any better but it will be easier on your leg to hold the brakes at a stop light without the car crawling up to nudge the car in front of you.
I have driven customers cars with discs and a big cam where no mater how hard I stood on the brake pedal (which has a 6:1 ratio) the car crept forward (bad combination of brake parts and poor cam choice for the street).
In the case of bad brake part choice they had retained a manual brake master cylinder when they added the power booster. There wasn't enough line pressure to fully activate the disc so only the rear drum brakes were holding or stopping the car. The big cam never generated enough manifold vacuum to power the diaphragm (it is the pressure differential between manifold vacuum and atmospheric pressure that makes the power assist work). In that case I took the power assist off the car as it wouldn't work with his cam and put everything back to manual with a smaller cylinder bore for disc brakes. Disc brakes require a minimum of 700 psi to even move the discs into contact with the rotor, 1,200 to begin to create friction. The pad composition at these manual brake pressure levels will also affect how well the car holds at a light. As does the heat in the system, as high performance metallic disc brake pads work better the hotter they get, stone cold they will barely hold.
There are a lot of variables to consider besides appearance when dealing with brakes. I am an engineer that also have had my own mechanical repair and Hot Rod shop to pay for my racing hobby. I research all of the variables involved before I buy the first part, as your brakes actually working are kind of important. I always follow the factories lead unless I am building an out right race vehicle, after which I look to the type of brakes used on other professional race cars (NASCAR, NHRA, SCCA) for the kind of racing I want to do.
I would recommend contacting Wilwood or Baer if you want to buy race car parts, and the Chevy Assembly manual for part numbers of the pieces that Chevrolet specified originally if looking to drive on the street. Since disc brakes didn't appear on full size Chevy's before 1967 you will need to look at 1970 and up to 1976 (when they went metric) for matching part numbers you can buy today.