Seems to me that the skiffs are fastest. I have raced a 505, Flying Dutchman and Tornado (to compare). The 505 and FD are not that fast relative to the quickest. E and A scows will kill them even in a sea. The A-scow is fast, but I would bet it would be 25% slower than a skiff because the skiff is close to a Tornado according to the Aussie postings I have seen and the A-scow is not unless there is no wind. Also, my experience is that a Tornado with only the main up will tie the best sailboards around a course, but that the shortboard speed sailboards are a lot faster on a reach.