I have rarely used a A2 merc for more than a minor meat shield and a useful aura. I try not to depend on them to do the killing for me. My major concern most of the time is for him to stay alive. I don't think it is the over all best setup from a min/max standpoint. It is however the ideal setup for how I play:

Weapon: Eth Reaver
Helm: Eth Up'ed Gaze (UMed)
Armor: Eth Up'ed Shaft (UMed)

Depending on the character I am using I can switch out the weapon for a Doom Cryptic Axe if need be.