I (and im open to correction here) always thought the std nyloc nut was 8.8 as you say, they can be sourced in 10 and 12 as well if you want high tensile nuts but they are heat treated to get to this, altho im sure plenty are chuffing them out at 4.8 in the far east...I agree that they seem standard, but the 8.8 means a ultimate strength of 800MPa, with yield at 80% of this. To get this strength the material has to be hardened so they are high tensile.