So in general is a 2"OD stronger than 1.414" width/height?
I built a simple calculator real quick. Here's what I found:
2" Solid bar 4' long in bending with a load of 3000N will only have a stress of 284.19MPa.
1.414" Solid Square bar 4' long in bending with a load of 3000N will have a stress of 473.69MPa
What about an I/H beam design?
(I want to go down in oraller history like Rudolph)
Carbon fiber I beams
I thought anything with rounded structures faired better under stress than to have corners (stress risers)
Carbon fiber for one, isn't a long term solution. Every time it deforms, it breaks bonds and degrades. If you're using it only in a torsional application, it works pretty well. Bending and tensile it is still alright. Compression is doesn't love.
And I-beams are better in certain applications. This might even be one.
This is what I got for a 4' long, 3000N loaded I-beam that's 2" wide, 2" tall, and 1/2" thick.
It has a stress of 184.72MPa (which is the best yet). These hate torsional loading, but as long as you're not trying to get axle articulation (think off-roading style twisting), this would fight your bending forces really well.