I once again went down the rabbit hole two days ago on fiddling with performance settings and finally got something I'm happy with. I also banged my head a few more times on the "Greased Palms" mission (the postal facility), failing each time and finally taking a break from the game.
I've now installed the "In Game Menu" mod which allows access to all eighteen missions. "Greased Palm" was the ninth in the campaign and I realized that I was going to start disliking the game if I couldn't unlock any missions past that. However, with the mod I can now play all missions, which means I can now access the other 50% of the game
