From what I can tell, Attack potency is not factored into Blood Weapon, every attack (GCD or oGCD) replenishes the same amount of MP. So Low Blow, Plunge, Carve & Split, Reprisal.. want to use all these during Blood Weapon preferably, as that's properly 'min/maxing' that CD. The better the MP replenishment, the more Dark Arts buff'd Souleater, Dark Passenger, and Carve & Split that can be dished out.

Like DPS using BfB, also consider 'holding' on popping BloodWeapon until the GCD wheel is at 75% or higher. This may squeeze an extra GCD into the buff's duration.