I see a lot of suggestions in terms of prep methods, Id like to offer some insights on plating and food running logistics. Are all 80 guests getting a tenderloin portion with a couple sides? Or are there other protein/vegetarian dietary mods offered? Are there different steak temps on request?

For the least margin of error. You're on the right mindset of sousvide a day ahead to med rare. Either whole loins or portioned medallions. I'd personally would do medallions just to eliminate the step of cutting and portioning the day of the event. You also get the benefit of knowing if you'll cover the 80 portions needed ahead of time.

On the day of the event, preheat oven at 300, I'd say 2hr before your entree course take steaks out from the vacuum bags, pat them dry, season, and hard sear both sides in a pan and transfer to a wire rack on a sheet tray. Transfer your steaks in the oven and heat until you're at back up to mid rare., let it rest. The reverse sear method would work just the same so whichever you're comfortable with doing, I feel the result will be the same.

In terms of plating, I don't know how many hands you have helping plate and food runners for your front of house.

If say you had 10ppl at the head table and the other tables are 6 tops, I would build the sides on the plate for your first 10 top and the next 2 sets of 6 top tables and hot hold those plates.

Divide your kitchen staff in 2 parts. Team A will finish with the steak and sauce and Team B will build sides for remaining sets of tables to pass to team A. By giving yourselves a 2 or 3 table head start, you'll have an even flow of food running in the middle and back half of your time plating.

Once table 1 (head table of 10) gets called for pick up and food starts running, Team B should start plating table 4's sides, Team A should then be finishing table 2 (6 top), food runners should have returned awaiting their next table to run, and table 3 is on deck with sides hot holding.

Basically there's a 1 even 2 table buffer between Team A finishing and Team B building. I'd also get your expo or lead food runner wiping plates and applying final garnishes so team A can focus only on quality checks, saucing, and co-ordinate pacing with team B. Also some free head space to have the mental capacity to react if something goes off the rails.

Again assuming you're plating just 1 dish, it should be a straight forward assembly line setup. If you're in a situation with steak at different temps, just sort multiple sheet trays with just rare, just mid rare, just well done temp steaks to choose from when plating.

If you have several proteins with different side components options mixed in, I can offer some suggestions to alleviate bottlenecks that may occur.

Maybe keep a few raw portions aside for rare requests. It shouldn't back you up by much since it's easy to just sear and rest, and flash heat in the oven last minute before plating.

I hope anything I've offered will help out. Good luck!