What about Delphinium or larkspur? they like to bloom in cooler temps but have pretty fernlike foliage (similar to astilbe) and I think they both tolerate full sun. I don't know if they will tolerate the heat, but if they can it would be a nice way to extend flowering into your winter or start early in the spring while having a similar growth pattern?
I would love to have your conditions to grow amazing lavender, that's what I would do.
Just as an aside for readers, if watered regularly Astilbe will grow beautifully in Full sun in NY. My neighbor has them lining the south west path to their front door and they are gorgeous.. but their sprinklers come on every dawn. And it's NY.
