Good info, I gues my 20 to 40 was a little out of the ball park... Bruce says 3 to 5 is too high!
Think of it as the line at the bank (if anybody ever waits in line at a bank anymore): if you've always got 3 to 5 people waiting in line, you need to hire more tellers. On the other hand, if nobody's ever in line, you're paying a teller to do nothing. (Less of a problem in a server than in a real bank, of course.)
pjm