Hey STEPpers, I don't know how much of this problem is caused by my own ignorance, but Dual Sheath Redux causes Skyrim to crash at a very specific point - the same one described in this ancient post. The second time Alduin breathes fire, BAM! CTD. I determined after heavy trial and error that none of the fire or spell effect mods had anything to do with the crash. DSR was properly patched and was last in the load order as prescribed by the STEP guide, BOSS was run, Wrye suggested no other problems were responsible. To solve this I just got rid of DSR. I'm sure that there are more elegant methods available to those wiser than myself, but at my level of non-skill, I'd rather have the rest of the game without fancy sheathes than endless CTD. ;)