I understand usually a quarterstaff is usually treated as a double weapon with 1d6/1d6 - however it seems like regripping it should allow use as a two handed weapon using only one end to get more out of using power-attack with it. However shouldn't that change the base damage too? If so to what?

1. Do stats for wielding a staff that way exist already?
2. If not, what's a sensible way to deal with it?

More info for 2:

The blade-weapon damage progression goes from 1d4 dagger to 1d6 short to 1d8 longsword to 1d10 bastard to 2d6 greatsword.

Wood-weapon damage goes from 1d4 stake to 1d6 club to 1d6/1d6 quarterstaff to 1d10 Greatclub.

All other martial 2HW with 1d8 damage have some special properties. Would it be balanced to allow a quarterstaff wielded like a 2H sword 1d8 damage? Probably not as a simple weapon, since most wizards don't use both ends of the Quarterstaff anyways due to lack of TWF, so this would grant them all a +1 to average damage; but it seems fine for characters with martial proficiency, given other options available.

Context of question

I'm asking because Quarterstaffs are the only free two handed weapon, and I got a bunch of guards who were robbed wandering unarmed through the forest. Most grabbed sticks as clubs, some got quarterstaffs - but one of them took power-attack/cleave/pushing-assault and wants to make good use of that. I'm considering letting him grab a greatclub, but at 50 sp value "crafting" one would take actual time/skill - neither of which they have. And 1d10 is considerable damage. So maybe use small tree as improvised version of Greatclub (-4 to hit), but his bonuses are low already, especially with powerattack. Thus 2H non-double quarterstaff seemed like good idea.

I understand usually a quarterstaff is usually treated as a double weapon with 1d6/1d6 - however it seems like regripping it should allow use as a two handed weapon using only one end to get more out of using power-attack with it. However shouldn't that change the base damage too? If so to what?

1. Do stats for wielding a staff that way exist already?
2. If not, what's a sensible way to deal with it?

More info for 2:

The blade-weapon damage progression goes from 1d4 dagger to 1d6 short to 1d8 longsword to 1d10 bastard to 2d6 greatsword.

Wood-weapon damage goes from 1d4 stake to 1d6 club to 1d6/1d6 quarterstaff to 1d10 Greatclub.

All other martial 2HW with 1d8 damage have some special properties. Would it be balanced to allow a quarterstaff wielded like a 2H sword 1d8 damage? Probably not as a simple weapon, since most wizards don't use both ends of the Quarterstaff anyways due to lack of TWF, so this would grant them all a +1 to average damage; but it seems fine for characters with martial proficiency, given other options available.

I'm a player in a campaign where we rescued a bunch of guards who were robbed wandering unarmed through the forest. I asked the GM if I could "help" him with designing the guard NPCs. While designing them I grew a little attached so I wanted at least one cool battle with all of them in it. Thus they need weapons. 

Most grabbed sticks as clubs, some got quarterstaffs, as those are inexpensive/free and thus can be quickly crafted along the way using the Craft rules - but one of them took power-attack/cleave/pushing-assault and wants to make good use of that. I'm considering letting him grab a greatclub, but at 50 sp value "crafting" one would take actual time/skill - neither of which they have. And 1d10 is considerable damage. So maybe use small tree as improvised version of Greatclub (-4 to hit), but his bonuses are low already, especially with powerattack. Thus 2H non-double quarterstaff seemed like good idea.