Is the size of the engine within the range given by the boat manufacturer?
Is the 5700rpm at Wide Open Throttle and is it within the manufacturer's WOT range for that engine?
And that figure is obtained with the boat/engine correctly trimmed & carrying its normal load?
If you change the load it will change the WOT rpm & it may need a change of prop to bring that back with the range.
If you corner too sharply & too fast then at some point it's likely the boat will start to skid sideways resulting in chine walk & hooking. That's driver error.
You might find this precis of the MAIB report into a double fatality at Padstow worth a read: http://www.mby.com/news/padstow-rib-...-released-1808
I'm inclined to think that your extra large load and its positioning made it that much worse when it did break away.
May also be that the speed & the lift ends up with so little of the hull in contact with the water that even in a straight line it can make the handling unpredictable & hitting a wake or wave could cause unexpected problems.
Being a cathedral hull dory I notice this on my own boat & it's a too fast for the conditions issue.