While it would hardly be broken, one way to make good use of power staves would be to take advantage of the fact that, while they use touch attacks, they're still weapons.
Hume Holy Knight 20
Ability scores at 1st level/20th level (25-point buy):
Str 7/7
Dex 17/22 (item for +5 inherent bonus), 28 if using gloves of dexterity +6
Con 13/13
Int 10/10
Wis 7/7
Cha 20/30 (item for +5 inherent bonus + leveling bonuses), 36 if using headband of charisma +6
Weapon in question: +4 shining burst holy staff of distance and speed (or a +5 if you're okay with just shining instead)
Feats:
H: Exotic Weapon Proficiency (power staff)
1: Point- Blank Shot
3: Precise Shot
5: Weapon Focus (power staff)
7: Rapid Shot
9: Improved Critical (power staff)
11: Snap Shot
13: Combat Reflexes
15: Improved Snap Shot
17: Improved Precise Shot
19: Greater Snap Shot
Those are all the basic ranged attack feats that would apply (Manyshot doesn't work because the projectiles aren't arrows, and Deadly Aim doesn't function on touch attacks), with some other feats thrown in that might be helpful. With the Holy Knight's Divine Sacrifice ability, a full attack would deal 11d6+51 (~89) holy damage per round when within 30 ft. (~86 without it), not taking critical hits into account, each hit having an attack bonus of +32, +35 on attacks within 30 ft., +42 on AoO, against the enemy's touch AC. Increase the damage to ~92/~89 and the attack rolls to +33/+36/+43 if you go with a +5 weapon instead. If your GM is a stickler and says that you need to have an MP pool to be able to take the proficiency feat, then drop Combat Reflexes or Improved Critical (your choice), move the rest of the feats up, and have EWP and Wild Talent as your first two feats.
Basically, you get an infinite ammo cheat (sort of) on Holy Hand Grenades. You'll be fine for hit points even when using Divine Sacrifice, because you'll have more uses of Lay On Hands (23!!!) than you'll know what to do with, and your damage goes up even more against evil guys (especially undead and dark knights) on top of that. If you go one further and use Smite Evil, any undead, evil fiend, or evil dragon will get RIGGETY-RIGGETY-REKT, SON when you're doing another 80 damage on top of all that. This isn't taking potential vulnerabilities into account either.
Hume Holy Knight 20
Ability scores at 1st level/20th level (25-point buy):
Str 7/7
Dex 17/22 (item for +5 inherent bonus), 28 if using gloves of dexterity +6
Con 13/13
Int 10/10
Wis 7/7
Cha 20/30 (item for +5 inherent bonus + leveling bonuses), 36 if using headband of charisma +6
Weapon in question: +4 shining burst holy staff of distance and speed (or a +5 if you're okay with just shining instead)
Feats:
H: Exotic Weapon Proficiency (power staff)
1: Point- Blank Shot
3: Precise Shot
5: Weapon Focus (power staff)
7: Rapid Shot
9: Improved Critical (power staff)
11: Snap Shot
13: Combat Reflexes
15: Improved Snap Shot
17: Improved Precise Shot
19: Greater Snap Shot
Those are all the basic ranged attack feats that would apply (Manyshot doesn't work because the projectiles aren't arrows, and Deadly Aim doesn't function on touch attacks), with some other feats thrown in that might be helpful. With the Holy Knight's Divine Sacrifice ability, a full attack would deal 11d6+51 (~89) holy damage per round when within 30 ft. (~86 without it), not taking critical hits into account, each hit having an attack bonus of +32, +35 on attacks within 30 ft., +42 on AoO, against the enemy's touch AC. Increase the damage to ~92/~89 and the attack rolls to +33/+36/+43 if you go with a +5 weapon instead. If your GM is a stickler and says that you need to have an MP pool to be able to take the proficiency feat, then drop Combat Reflexes or Improved Critical (your choice), move the rest of the feats up, and have EWP and Wild Talent as your first two feats.
Basically, you get an infinite ammo cheat (sort of) on Holy Hand Grenades. You'll be fine for hit points even when using Divine Sacrifice, because you'll have more uses of Lay On Hands (23!!!) than you'll know what to do with, and your damage goes up even more against evil guys (especially undead and dark knights) on top of that. If you go one further and use Smite Evil, any undead, evil fiend, or evil dragon will get RIGGETY-RIGGETY-REKT, SON when you're doing another 80 damage on top of all that. This isn't taking potential vulnerabilities into account either.