Been looking a bit more at this and nearly answed my own question
(HighDmg - LowDmg)/2 + LowDmg) / Speed = Avg DPS
So where would "base dmg" come into this equsion?
(HighDmg - LowDmg)/2 + BaseDmg) / Speed = Avg DPS
Maybe?
or would that not give a true avg dps either?