I am running Ford dual piston calipers up front and chevy half ton / three quarter ton disks in the rear. I have been told bigger is better in terms of masters.
Very common misconception on the net.
As small as possible without hitting the floor will provide the most braking pressure you can get.
As in you try as small as you can, and move up as required. You booster is to small, and not matched for a 1.25" master. You will have less then satisfactory pressure with that size of master.
If you cant move the volume with the smaller master, and end up with a 1.25, you will require a bigger booster, or hydroboost to get back into the good pressure range of 800 plus PSI.
The bigger master only moves more volume. It does NOTHING to improve braking power, and actually does the inverse when used on the same booster that was originally equipped with a smaller master.
The worst advice on the net is almost always the brake mod threads.
just to clarify. The large master will work. The difference is, working, or working good/properly.