I would say that pressure is in between. Why not buy the taller piston and fix the issue, then if you decide later to add a brake or turn the pressure up more, you won't have to take the trans apart.
IMHO. Most brakes are 170-200 psi that I know of. My old turbo action manual shift was 125 psi. I would go with a 3.8 lever too just in case. I know Paul Forte of turbo action told me with 190 psi he recommends a 3.8 as anything higher is too aggressive at that pressure.
