You're right: consistently being 6x faster on the buzzer than the common case for your opponent is going to let you destroy them. Their only hope is that you can't come up with a response before Alex finishes reading the question.

I arrived at the 6x approximation by googling around for avg. ethernet latencies. I'm consistently seeing numbers of .3 - .35 ms for an ethernet ping/pong. I think it's fair to assume that with the money IBM has invested in this, Watson is on at least ethernet quality connections.