If itsall adults, you have to look at something close to a quarter pound per person, 25 lbs, and you need to be the person doing the potioning that nobody goes short. Eye of Round is about the toughest cut to work with, so my thought would be that you would either braise it or cook at a pot roast; in the latter case I would suggest dutch oven or slow cooker cooking, at around 285 for three plus hours (based on my use of 3 lb roasts, probably longer) after covering with a can of beef consomee and a tall boy can of dark beer and seasoning (S+P, garlic, onion and the like) A hundred people is pretty challenging, so I'd ask around some more!

http://allrecipes.com/PersonalRecipe/62549907/Slow-Roasted-Beef-for-Sandwiches/Detail.aspx You need a remote meat thermometer inserted in one of the eye of rounds. If all roast are equal size/weight or close to it they will be done equally. See this recipe for details.

Eye of the round is a good quality/lean cut of beef. It has a great flavor/texture if cooked correctly with some liquid.

do you have to use eye of the round-little tough, grainy and dry, but cooked low and slow with some basting might help. Cook it in beef broth with some onion, garlic, and a bit of BBQ sauce. Amount per person? Depends on other dishes, is this the only meat dish?

also adding a splash of vinegar to the beef broth with help to tenderize meats, it will not taste of vinegar but it does help with the texture.

I would do the PR posted by bd.weld. Just made it again the other day. So tender and juicy. I do add different things, see my review. This time I seared then basted with a lil more evoo and generously sprinkled with Herbs De Provence.