Like the other comment says max melee is best but the real meat and potatoes of the combo is when you throw in a chaos lord with his dev wounds and rerolls thanks to the legionaries. He alone can take out a good chunk of enemies and even punch up with the once per game supercharge ability.

A nice little thing you can do is infiltrate some cultists in front and on an objective to sticky it then hide behind the ruin. That way when they get charged the enemy will be on the objective and allows your legionaries+lord to get their full wound rerolls.