I think Monte Warnock did time one of 'em one day -- but it was a few years ago. And it wasn't a regular unit, but rather a handicapper one. They've got bigger doors, and the wind blew one open. It was raining as well as windy, and the rain made for a slippery course. He SAYS (
) it went though the lights at about 7 - 8 mph.
As for how fast do we tow -- usually no more than about 15 mph. Not only do we not want to make any blue spills (sure hope they're blue, not other colors) from splashing, but also we try not to wear the runners on the bottom of each unit - as might happen from too much speed while under way.
Didn't think I'd have an answer, didja?