Maybe if I just focus on the main mission(s) of the open-world areas and just do the main story missions I might be able to plow through the game a lot faster, but where I currently am in the game I can't say whether or not skipping the seemingly less important stuff could bite me later on. Looking online I apparently only have 2 more main story missions to do, so I might be able to finish this playthrough at 60 hours having done most if not all of the side stuff.
I've been carefully tracking my power and xp/level gains from quests this playthrough in an effort to make a written record of the most minimalist playthrough possible. I hope to post it when I am done, to assist other people who want to play a bajillion times with a lower playtime for each go or people who just want to keep it to the most interesting non-main quests. I am doing this on Nightmare so it should be feasible at any difficulty.