For the Erynies: Maxim+Maxim; Trebuchet+harpoon.
8 maxims give the shield damage of 4 Subachs, so it's like flying a Perseus with an all-Subach armament, only with much higher projectile speed, and much longer range. With good aiming, you can splash a Mara before it can shoot back.
The Trebs properly used will give unshielded targets 3 km away, perfect for shooting with the Maxims (single fire prefered, shooting continuously sucks batteries too fast) before they can do anything.
And the Harpoons are as a backup weapon, in case any fighters manage to avoid the Treb with their name on it.
For the Perseus: All Kayser; Treb+Harpoon.
With this ship, it's best to use single fire mode for the missiles, a-burn close to a damaged target and finish it quickly with the primaries. With dual fire the Trebs run out really fast, and a single one is more than enough for any fighter charging at you.
And the GTF Pegasus:
Subach for primary, 3 Trebs+4 Harpoons, or all Harpoons for secondaries.
With 3 Trebs and some luck you can have a wing of 4 Maras changed into a wing of 1 Mara and 3 flying pieces of junk, and you're able to shoot all 4 down easily without backup.
With the All-Harpoon loadout it's good to have some friends because you won't have the advantage of superior range, but you'll be able to challenge 2 or 3 wings of enemies before running out of missiles.