Not sure about Zone 6 or 5 but, I live in zone 7 across the street from the beach. I have the "Miss Huff" version in the front and the yellow variety in the back. Sorry if it doesn't help.

Not aware of any offhand, but they are working on hardier varieties every year. That being said, my 'Chapel Hill' lantana--reported by Dirr to be hardy in zone 7, did not return this year. I did not mulch it as heavily as I might have, so I'll try it again...it was beautiful paired with 'Homestead Purple' verbena!

Also FYI, I did not often see hummers using my lantana...maybe once or twice.