I believe you will find Dark Melee/Invul to be way tougher with the same slotting, or tweak it for even more performance. Dark Melee and Willpower have no Synergy. Dark Melee gives attacks that give health and endurance, which Willpower does not need. The Recharge bonus you put in will not affect Willpowers Uber Buff Tier 9, nothing does. With Invulnerability you have tougher armors, def debuff resistance, and the global Rech brings your tier 9 around faster, also brings the heals and end recovery faster which Invul + Fighting armors need. Invul is an end hog as we all know. The Synergy between DM/Inv is truly neat.