Baldur's Gate : The Sword Coast Chronicles : NWN2 Persistent World

The Goristro form doesn't get any bonus from an equipped weapon before changing to it. Dryad and Planetar work.

... Isn't the goristro an unarmed shape?

He's got a greataxe. Also, the wiki says it has Power Attack, but there's no mode bar for it.

Also, in general, items granting saves bonus are not applied to shapes shifted to ? It's a weakness, though maybe there for balance.

Item skill/save stacking is disabled when polymorphed, due to technical constraints on how the item properties are merged into the creature hide. Those constraints could be worked around, in theory... but as you might imagine, there's not a lot of interest in doing that right now.

No idea about the rest, though...

Sometimes the Dryad is good for higher AB, but, all-in-all, the Planetar is The form to use.
It's sad about the Goristro without buffs to his greataxe. I like its attack animation (as well of the minotaur), I use it sometimes, even though it's got 6(?) AC less than the Planetar.

It's probably missing MergeW in polymorph.2da

Speaking of Planetars, why warlocks turn into lawful good celestial beings in the first place is really a whole issue in and of itself.