I've done hundreds of staffed-station buffets with both steak and chicken offered.
My rule on the proteins (and mind you this is VERY general--depends on a
number of factors concerning the guests, time of day etc too) is 120% when serving
a single protein choice, (to allow for seconds, surprise guests, etc).
And 115% when serving 2 choices. Now, that's 15% over for each, so 65% for each entree,
rather than 50-50. This way if there's a big "run" on your yummy steaks, you'll have enough,
while you'll have lots of chicken to take home. Or vice versa.
People aren't an exact science. Hauling a guesstimated amount of food overage to the party
is an integral part of catering. The cardinal rule being....you never, EVER run out of an entree.
(not that I'm hereby stating I never HAVE.....no, no, no, neither confirm nor deny. )
And welcome to Cheftalk!