Limits of 28 spline axles

[351 82GT]

At what point are the factory 28 spline axles not strong enough? I have about 300rwhp with 1.7 60' times.
What is their breaking point?
In retrospect, I SHOULD have gone to 31 spines when I had my 4:10's put in.

 

[bluevenom867]

I dont know about factory 28 splines...but the number of splines for that amount of power has no problem being only 28 for aftermarket axles