What level was you character?
Do full sets of armor have their own buff?
Don't remember I just reached 80+ so less than that since it was days ago but my stats were mostly all in on Wood because the Ring Pommel Sabre mainly scales with that. The rest of my Virtues were to meet Spell requirement
The main thing is staying at full health to do 13% more damage with Man of Benevolence set, and keep negative effects on him
I have Power Gain on gloves after Deflecting Critical Blow, which seems to be the strongest version of it at like 15% more damage, and the longest lasting
Since Power Gain doesn't stack and not all are the same, weaker versions get overwritten, so I put Damage Amplification from Martial Arts on weapon and Wizardry
Spell on headgear
Also if you want to use Life Wither on him off the horse, time it the second after he starts a Critical Blow
Because his damn Fire Enchantment removes Damage Amplification
And for the hell of it, this is at level 88 with a +6 Glaive testing out Overpower Burst