How to optimize a lucky egg?

You can get around 80 or so evolves during one egg. So just count them all up and see if you're close to that. You could also coordinate your eggs to hatch at the same time.

I evolve like 70 Pokémon per lucky egg.

Time it so you get your 7-day streaks and all your eggs hatch, and then evolve about 70-80 whatevers. Depending on eggs and evolves (new dex entries), you can get close to 100k XP.

have 85 pidgeys ready, 1020 candies. I evolve around 80. -1 depending if i start with a first 7th day pokestop.

Depends on how fast you are. You should easily evolve two in a minute, which makes it 60 during a Lucky Egg. If you are fast you should manage 70-80.

Also, you can use more than one device and evolve even more. I usually use two, but I suppose you can use more, especially if someone helps you.

I get 85 pretty consistently (the past three eggs), but it seems like I always fat finger something at least once, so I'd guess I could get 86. Just hasn't happened yet.

Especially if you have 85/86 pidgeys ready to go, you can just align the top most pidgey with the evolve button after sorting by # and you should be able to whip through them without scrolling.

Step 1: Enable lucky egg
Step 2: Start evolving Pokemon
Step 3 (Optional): Stop when lucky egg wears off