The Mattock is great, matched with the Widow, Phalanx and GPS, but every shot has to count to cut down on wasted shots and the loadout could get tricky to use in very few fights, like the Object Rho fight in particular.
The Revvy is another option for max damage and it works best with Hardened AR.
So I'd guess the key powers for max damage are:
Heightened AR -|- Hardened with Revvy
Commando (15% to power damage and 15% to weapon damage)
Inferno and Heavy Disruptor -|- Heavy Disruptor and Heavy Warp ammo -|- Tungsten and Heavy Disruptor
So you could also take and fully evolve Reave if you stick with Inferno and Heavy Disruptor, but Improved GSB gives that extra 10% to weapon damage also.
Here's a calculator you can use:
http://mass-relay.co...ents/calculatorArmor pieces also provide a minor bonus. So you could go with:
Recon Hood or Kestrel Helmet
Kestrel Torso Sheath
N7 Shoulder Guards or Amplifier Plates
Stabilization Gauntlets or Kestrel Arm Sheathing
The leg pieces would be your preference, with Stimulator Conduits, Ordinance Pack and Kestrel Power Pack as the most tempting to go with.