Sure, the numbers are done via simple cantilever beam bending equations... the formulas are pretty simple, but theyre the same sound engineering methods used by professionals - a friend of mine is a very experienced structural engineer, so i often run things past him and he has taught me alot over the years...
The equations are identical for square beams, round beams, any shape beam... only the section modulus changes from square to round, so the proportional differences will be the same from carbon to glass no matter which sectional beam you choose to use, square or round. Square sections do have a higher section modulus than round as you already know. So naturally it will be slightly more effective. Building up from a square section spar to round only at the bearings in solid glass seems a simple low cost route - i like it.
What i dont know, is how much load the rear section must carry from the sail track pulling on it? If you use thin skins as a front and rear fairing, this may be an issue - although my gut tells me this isnt a very large load because its spread over the entire length of the mast...
I didnt compare the larger carbon section, because the goal was eliminate most of the carbon for cost reasons and the difficulties with infusion of it. The idea was to come up with a way of reducing the cost of a twin unstayed biplane rig - seems to be the biggest drawback of this rig - the cost is very high even if built yourself. Im up for $10k minimum for the 2 masts, then i have 2 battened mains, 2 booms, 2 sets of bearings etc. Its getting very expensive real quick. Hence a solution with much less carbon...
But Naturally, it will become much stiffer and the wall thickness could be reduced further if the larger section was done in carbon. The point of diminishing returns happens when the wall gets so thin that buckling determines the structural design and not the bending.
As to running the numbers... the numbers dont mean anything unless the loads are well defined and the material properties known. That is, garbage in = garbage out... The numbers used above were simply for comparative reasoning between 2 materials, carbon and glass, so if your looking to compare actual weights to what your already using but in a different configuration, then all the design loads and material properties need to be identical for each calculation. We dont need to be this specific in making decisions on which way to go about building something tho, all we need is the comparison and we will know what percentage difference there is in terms of weight and cost... Obviously, carbon will always be more expensive than glass, and always lighter too... question is, by how much... and thats the whole point of this exercise...