@Humpleupagus @Twig @magicalthinking For me it's the album deliverance. They hit the watershed (no pun intended) of their music evolution in the middle of that attempted double album.
You can almost tell the moment of time they were told they weren't going to get the double album release as you listen through it. The music goes from tight thrash with slick engineering to a looser less polished sound. They never put as much effort into the studio sound after this release.