when a breaker is listed as 2,3pole on a 277, 480 panel, this means it can be used as overcurrent protection of a 3phase 3wire 480 load or a 1 phase 2 wire 277 load (never done this, but make sence to me.

If you only use to hole of a three wire breaker does it matter which two hole you use? I thinking about the balancing of all three phases in the panel. -thanks

Doesn't matter in your scenario. 240.85 comes into play on non-solidy grounded systems though, such as high-impedance grounded, corner grounded, mid point phase grounded and ungrounded.