[Burpee]

Once again. Ductile vs. Brittle. Has nothing to do with a duck on a floor eating peanut brittle.. On applications where a bolt catches hell ( leaf springs, shackles, heavy spring mounts, heat-manifolding), grade 5 is the go to.Why ye bleateth. Resitance to multi-directional flexing.
I like to think of Tensile ratings as torque-ability. Rod bolts, head bolts, blade holding bolts etc.
Right or wrong ? Not sure. A mechanical engineer who designed locomotive parts put it to me this way. 5160 steel at 60 rc. vs 5160 @ 50. One is a blade the other is a spring. Simple enough.