The fastest boarding I've ever experienced was something Cathay Pacific did a few years ago. In the boarding area they had three lines with a bunch of section signs and an a couple employees hassling/sorting people between the lines. The rear of the plane sections were at the front of the line. I'm guessing they were just counting how many people were in each section?
Either way, when they opened the doors, they just picked one of the lines and the employees walked down the line scanning everyone's boarding pass and then the whole line proceeded to board the 777 (dual isle). Then they repeated the process with the next line after a short pause.
Which works out to back to front boarding of 1/6th of the passengers in a section at a time. When it was my turn the entire line pretty much just walked onto the plane bumped around a bit in the section and sat down.
Quite a shock given the hour long boarding AA can sometimes pull off with their messed up boarding order based on miles and cabin front to back...