I'm not sure why folks are saying the boom isn't there, I see it. It also looks like before the capsize you're running with the traveler somewhat in with the sheet bagged out. I would have dumped the traveler more earlier and maybe not as much sheet. The rig looked a little loose from what the headstay was doing, tighten up for big wind, also rake the mast back for a day like that. I have found sometimes that cranking the jib in (oversheeting it) can help stall out the main if you're looking to slow down. But, if you're going downwind, speed is often your best friend.