My guess would be that this is one of the newer interspecific hybids (zonal-ivy crosses) of Pelargonium. It looks a lot like 'Caliente Fire'. I've grown 'Caliente Fire' before and that would be my best guess for your plant. I've seen them sold a lot in the last few years and they are much more floriferous in the heat of the south than the pure Ivy Pelargoniums. Your plant is lovely! That being said, I'm not sure where you'd correctly place it in your list since you don't definitely know the cultivar.
Storksbill (Pelargonium Caliente® Fire '09)
