I posted this in the other thread, but the brake pedal free play is very minimal, 2-3mm so it isn't that. (tested by pumping up the pedal until totally firm, then pushing on the brake pedal with 2 fingers lightly to check how far it will still travel, it will move about 2-3mm until it hits the first stop point, then you have to push really firm to get it to move a little bit more, still the total travel is minimal)
Also, after driving around with the new booster in, it really does firm up the pedal. There isn't a lot of nothing at the top of the pedal now that I've given it some time, I had to do the first test drive in the rain so that could have been contributing (wet rotors?) Overall I'm very happy.
-Steve