I do like your idea of the paraelemetnal magma over the fire elemental. I thought elementals and paraelementals where genderless. I do like the paraelemental more then the regular elementals except for the water elementals.
How would you make the description more like that of an Efreet but original? If I was to go with something less humanoid I would go with something like Ymeri form Pathfinder. I was thinking he use magic to gain that form permanently.