Can you use the Power Attack feat when doing this? Since it's an automatic hit, it would seem pointless not to max out the power attack aye?Description: A combatant can use a melee weapon
to deliver a coup de grace to a helpless foe. A combatant can
also use a bow or crossbow, provided the combatant is adjacent to
the target. The attacker automatically hits and scores a critical
hit. If the target survives the damage, the target must make a
Fortitude save (DC 10 + damage dealt) or die.