In the events I've been to, the taxi rank queue runs slower than the tube queue after the first flood of people chew up all the cabs that had been queueing. I tested this once as I did the tube and marked someone who entered the taxi queue at the same time as I started in the tube queue. I was rounding the escalators and they were still near the back. Purely unscientific, but I'm sold on the tube.

As others have reported the tube queue tends to move at a shuffle, but if you imagine shuffling that distance it doesn't take too horribly long. Remember that a full Jubilee line train can accommodate over 800 passengers. At off-peak times the line runs 24 trains per hour, so figuring that most trains are relatively empty coming west out of Stratford/West Ham (and a few originate at North Greenwich) that works out to being able to handle ~300 passengers a minute.