I thought the fastest was back to front, but alternating left and right side for each row. In other words, board the left side of last 10 even rows and the right side of last 10 odd rows at the same time, then let right/even, left/odd people in, then move on to the next 10 row, etc.

There was a research paper on that few months ago, and it was on HN. Does anyone remember details?