For the finest kerf and the best overal cut quality use the Fine Cut consumables. You can read the cut charts in your manual, 10 ga and 12 gauge are listed but you can adjust your parameters between these two.
Ret Cap 120928
Swirl Ring 120925
use 45 Amps, a .4 second pierce delay time, .120" pierce height, .010 cut height (yes very close!, should be around 68 to 72 arc volts) and a cut speed of around 90 ipm.
It is critical that the pierce height, pierce delay time and cut height are set accurately. Also, to get minimal dross, experiment with cut speed.....I would start at about 80ipm and do successive cuts at 5 ipm faster until the cut edge meets your liking.
Make sure your air is clean and dry!
Jim Colt Hypertherm