[Zanthis]

NSP III: 50kt, 3 reload, 60 dmg, range 5
PPB V: 30kt, 1 reload, 50-60 dmg, range 6

Assuming only 50 dmg for the PPB, these weapons perform as follows:
NSP: 0.4 dmg/kt/turn
PPB: 1.67 dmg/kt/turn

The PPB deal 4.17 times more damage. Now, the NSP skips shields and armor. A quick check on Daynarr's Sergetti reveals they run around 5% of their ships' kt armor and 20% kt in shield generator.

Assuming a ship is dead when only armor remains, the NSP must do on average 0.95 times the kt of the ship to kill it. The PPB, OTOH, must deal 1.2 times the kt to deal with the armor, and 1.875 to account for Phased Shields V, for a total of 2.25 times the kt of the ship to kill it.

IOW, the PPB has to deal 2.37 times more damage than the NSP to kill a ship. As we saw above, it does 4.17 times more damage.

YMMV, especially in the opening volley, since NSP's kill components while PPB's are still beating down shields.