Thanks so much guys for your input.

So, here are some options as I see them, either individually or in combination with each other:
1. I can use hemlock and red oak for all my posts. Looking at Will’s quick calculations this could get me over the hump of the high kneewall. This seems like a good idea no matter what, as there are certainly some harvestable oaks and hemlocks that could be used for this project.
2. I can lower the post height and kneewall by 6”, and then use 4’ braces along the long wall. This would leave me with a kneewall height of 3’2” (top of crossbeam to top of plate).
3. This problem is addressed in a couple of books I’m using, and one of the solutions shown throughout is using diagonal struts joining from the top of the tie to the upper ends of the posts. I could do that on the two end bents (wouldn’t really want for the middle bent for loft accessibility). I don’t know how this extra removal of wood in the post would subsequently reduce its strength, but the brace pocket would only be a few inches below where it joins with the plate.

The last thing that’s running thru my head, and I understand this forum won’t help me calculate this, is that the walls/insulation for this building will be straw bales with a earth/lime plaster. In a house this size (small single story), the bales could be structural in themselves. I am going to try and see if they can be relied upon to help prevent this spreading force at the tops of the posts.

timberwrestler, I’m not sure we’ve met, but I’d love to be lent a hand sometime. At least four braces will be cut from curved timber, and that will be a first for me. Also, some timbers may be hand hewn, and I’ve never worked snap-line layout before, and I’m sure I’ll have questions about that.

Thanks for all your input gentlemen; I am invigorated by this process. Makes me want to design my next structure completely (with some more practice and training of course),
Dan