I don't know where the 4500 pound requirement comes
This is probably an OSHA standard for holding a person from falling [5000 pound tension load].
That rating needs a
known span between between the hold downs, in normal sailing case, the
Stanchions.
The fact that it not a wire or cable, doesn't not relieve the safety factor of using a "Safety tether" hooked to the bar or life line cable.
Why so high a number, since normally who weighs 4500 lb?
It is designed to stop a "fall" of a normal person hooked to it and sometimes 2 people depending on the fall distance.
Scenario: Heavy seas, waves over the bow, hook your tethered safety harness to the
line or tubing.
Then a Big waves hits you and knocks you overboard.
Why does the
LOA table show different specifications of load?
I suspect this set by the distance between stanchions for smaller LOA boats.
Last safety note on Life lines...
In load spreading calculation, you would assume each
stanchion base hold down would need to support at least half of the load. In industrial safety world, each stanchion should hold down 4500 in worst case on a free fall [this is a dynamic load].
Since
freeboard, on a normal sailing vessel, is not much a free fall to water, I would suspect your stanchion hold downs should be
at least half the life line loading.
_____
@Maine Sail your tubing is more than adequate to hold > 4500 lbs
Jim...