the only real way to get the real numbers is to test it. climb pull it to idle, nail speed and when stabilized and passing an altitude start timing and hold speed. note altitude at 1 or 2 minutes in. climb back up and repeat at different speed. plug it in a spread sheet and calculate rates of decent for all timings.
every plane is going to different.
also, remember a windmilling prop will have different numbers than a stopped prop so the windmilling prop should give you a bit more safety margin with the circle.
i have not done the number for C/S at both fine and coarse pitch, but they should also give different numbers