Main thing to focus on with powerstance:
1. Pair large sweeping moves with powerful thrust moves
2. Use weapons with high damage and low weight (but shitty movesets) in L Arm
3. Us weapons with great 1H (but shitty 2H) movesets in R Arm
4. You still have access to both 1H movesets, so decouple your powerstance (or switch to RA2H) to throw out surprise R2s or projectile weapons
5. You get two rolling attacks. Use wisely.
6. Use a lighter, faster weapon in the R arm so you can set up combos (R1-L1-L1).
A good moveset looks like this:
R1: Fast Slash to stun
R2: Thrust to poke or slash to roll catch
L1: Slash to combo out of R1, or thrust to roll catch
L2: (never use)
R Arm: Short Sword, Sun Sword, Fume Sword (R2 thrusts)
L arm: Bastard Sword, Claymore, Mirrah Greatsword, Majestic GS (L1 sweeps, auto combo after R1)
R Arm: Any GS
L Arm: Lost Sinner's Sword (best UGS for power stance, use ivory warrior ring to shield break people in 1 hit)
R Arm: Uchigatana, Estoc, Rapier (R1 or R2 thrusts), Manslayer (poison infused)
L Arm: Warped Sword (4 hit spin, poison for manslayer)
R Arm: Longsword (R2 sweeps)
L Arm: Pike / Spear (L1 thrusts)
R Arm: Blue Flame (R2 casts)
L Arm: Moonlight GS / Watcher GS (L1 sweeps, auto combo after R1)
R Arm: Blacksteel Katana (R2 sweeps)
L Arm: Pike / Spear (L1 Thrusts)
R Arm: Heide Sword (R2 sweeps)
L Arm: Dragonslayer Spear (L1 thrusts, decouple for projectile)
R Arm: Ashen Warrior Sword (R2 thrusts)
L Arm: Flamberge (L1 sweeps, combos into bleed)
R Arm: Short Sword, Sun Sword, Fume Sword (R2 thrusts)
L Arm: Heide Sword, Varangian Sword, Long Sword, Possessed Armor Sword (R1 sweeps)
R Arm: Any Dagger
L Arm: Any Spear or straight sword
R Arm: Red Rust Sword
L Arm: Mastodon Greatsword (both use strength only scaling)
R Arm: Estoc / Rapier
L Arm: Washing Pole