It looks like you're new here. If you want to get involved, click one of these buttons!
I agree the 4" or 6" freeboard figures aren't that useful, but Clipper publishes the displacement at each inch, which is nice for comparison. I don't think the Itasca is in the same class as the Mackenzie, but I bet it would be comparable to the Sea Clipper in terms of volume (Wenonah's can be tricky with their razor-sharp entries that add waterline but not much volume).
My best guess would be that you could expect a maximum displacement of around 1400lbs, with about half of that being a comfortable/manageable load. A 17' Prospector can hold 600 pretty well, so I expect the Itasca could do this or a little more in fine style.