Length is all dependent on use which is derived from weight, power, trans gearing and most important the highest rpm the shaft will see.
What can't be done in steel can be done in AL and CF
This is beyond 72"
You could run a 72" shaft in STL at 4.5 or 5", however that will suck the performance from your truck turning that shaft, probably kill the t-case bushing with all that weight too and have speed limited rpm around 4200 or a few higher, which is right around the speed limiting of that 88" AL shaft.
And as
1pieceatatime said, over torque is usually a low speed break, rpm breaks are much more deadly as learned in a outlaw class a few years ago that you just don't throw CM in 3" at everything..... then thru the lights at 8k rpm and and the shaft comes apart because it was to long for the rpm and cuts thru EVERYTHING like roll bars, helmet, shoulder, head, face, arms, ribs, legs and barely leaving her alive....
As long as everything is looked at and calculated, there are alternatives.
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