When you start culling, work on the bottom end first. You said you have a lot, divide the number in half, and cull the bottom half. Now the ones that are left, should be easier to examine, to watch, and should fairly readily separate in to the pretty sure and the maybe's. Wait a week or two, divide the maybes in half, bottom half cull.
Wait another week or two, and at this point sometimes your decisions on the pretty sure changes, and a maybe may move up...but split the group in half. And a week or so later make your final decision.
A large group of roosters act differently. They have a lot of competition, when you start thinning them down, their personalities have more scope and often become more evident.
Good luck, I have had much better luck with this, than waiting for the best rooster to show himself. It just makes making the decision easier, if I do them in groups.
Mrs K