60% FTP for 90 minutes, my new aerobic endurance ride to gauge progress over time.
Guesstimated I need 30-minutes to warmup and tested that by hitting lap button on bike computer:
Yup 
Then looked at EF and decoupling over final 60 minutes:
Over time as FTP goes up I want to see increase in EF. Decoupling nice and flat, and under 1%.