My son built two of Dave Parker's Sumo NXTs, found
1) The robots are as strong as tanks.
2) Dave's light calibration program works well--in eighteen sumo "battles", neither robot ever ran out of the ring by mistake.
The robots were filmed at normal speed. (The gray tint of the video is because of a darkened room, to avoid ambient light interfering with the light sensors).
Ten points if anyone can guess the title of the video's bombastic soundtrack. :)