I don't have any Perry so can't help you there but
I mixed my Gorgon Gerbs(just got them based yesterday) with my Black Tree Gerbs this morning.They are maybe a MM smaller then the BT and slighter built.So mix pretty well.
I'm looking at a Gorgon Pole next to a Artizan Brit and they are about the same size.
Both 30mm from bottom of the integral base to top of the helmet.
Pete
BTW Artizan and Gorgon are both sculpted by Mike Owen if memory serves.