would a .36 caliber, 158 grain, semi-wadcutter, traveling at 830-850 FPS, hitting center-mass, be effective as a self-defense round
Yes of course it would.
I've put down horses, deer, hogs, etc using a 150 grn LSWC (non hollow point) out of my 642.
Using the same bullet out of a 4" Model 28 357, I've killed several moose and a buffalo.
I have all the faith in the world in the 150-158 grn LSWC bullets out of a 38.