John, generally speaking, the less HP you have, the less stiffness you need. So a 40 mm axle will generally be less stiff then a 50. A 28mm frame less stiff then a 32.
The Euro folks are now making 4 cycle, low HP karts. The tend to be 28 mm frames with 40mm axles. I believe Margay makes one as well.
We put a 206 on an old Intrepid 32 mm X 50 mm axled shifter chassis! There was NOooooo way we could free it up enough!! We just put an older TopKart with a 28 mm frame and 40 mm axle together- haven’t run it yet. But I suspect it will be MUCH freer!!! I’ll let you know next year!
By the same token, it’s very unlikely a 28 mm frame would work well with a Stock Honda shifter either!
Hope that helps. But I’m sure someone with a lot more knowledge then me could better answer your question.