Ok, I geeked-out a little here.

Using Quickload, I used the 32 S&W Long case, loaded it with a 115gr Gold Dot, set OAL to 1.169 to mimick the 30 SC useable case volume.

5.9gr of Power Pistol came up to just under 50K psi.

Here are velocity/muzzle pressure predictions:

3" bbl - 1222 fps - 12,051 lbs/psi
4" bbl - 1313 fps - 8,518 lbs/psi
5" bbl - 1375 fps - 6,513 lbs/psi

Baseline QL comparison - 9mm +P 115gr Gold Dot, 7.8gr Power Pistol, 37,714 lbs psi max pressure.
4" bbl - 1368 fps - 8,059 lbs/psi

[Linked Image from i.imgur.com]