A very easy fix for the cultist issue:
Go to your <game-install>/Data directory
Open WeapDef.dat in a text editor
Search for Laspistol
In this section change 4 to 3 under #animation
Change 2 to 0 under #number of sound effects for Firing
DELETE the two lines under it that give the file names for the sound files (something.wav)
Save the file, play the game - no cultist crashes.
Of course it will still have the occasional crash, so save often, especially before starting new missions it seems.