JoseC pretty much hit the nail on the head there. Don't do ZMI, if you're hardcore training, until you can use giant pouch. Otherwise, you won't be making a significant amount of additional xp.
ZMI from 75+ is the most efficient way to do it. You do it at your level but you will be losing a little bit. You can use all the time you saved doing ZMI by making double nats at 91.
