Engineer friend says to never replace G-8 with G-5 unless you have good reason and know the numbers--Grade 8 is not stronger than Grade 5 in all situations (shear vs. tension). He sez that Grade 8 will break in some circumstances where 5 would not...more brittle/whatever, where the 5 has a little more give.

Anybody know for sure?

FWIW, DP