7.5-15% Weak Spot Damage. Weakspot Kills also ignore Enemy Hit Mass.
1-2 Extra Chained Energised Hits and 2.5-10% Impact on Energised Hits.
Critical hit chance scales by your current heat level up to 27.5-50%. Also increases critical ranged attacks damage by 4-10%.
Up to 7.5-20% Strength scaling with Heat Level.
You can also run Sunder instead of Brutal Momentum on the Power Sword - which makes you better at cleaving mixed hordes with armor if you need to. I haven't messed around with it much but been told by other vets its another good option for Havoc.