Average Damage

I'm sword, so I take it this has nothing to do with me?

Minimum stab damage and minimum slash damage has the same value. Maximum stab damage and maximum slash damage has the same value.

It doesn't affect you, you can just use the original (max dmg+min dmg)/2, though the formula

[(STR * Slash multiplier + DEX)+(STR * slash multiplier *0.9 *mastery + dex)]*0.3 + [(STR * Stab multiplier + DEX)+(STR * stab multiplier *0.9 *mastery + dex)]*0.2

should work and give the same result. The way to get the result is just way more time-consuming.