Even without a combo counter, you can one shot with heavy attack on any infested creature. Wind up speed is for when you want to use heavy attack to break the Necromech fast. Change to Radiation damage to deal more damage for Necromech enemy, however it only takes 2 shots to break an arm off anyways. That's what the wind up speed thing is to help you do that quickly. While running this build with a 12x combo count, heavy attack managed a 4,454,725 Impact damage critical on an infested enemy with [Voltaic Strike] and [Virulent Scourge] instead of [Shocking Touch] and [Primed Fever Strike].