My name is Nicolò i'm live in Venice (italy) and i I am a fan and collector of palms
I would like to know if you have to sell hybrids as Jubaea x
Syagrus, butia x Jubaea,Jubutiagrus, Butia x parajubaea , Parajubaea x Jubaea
my contact are: firstname.lastname@example.org
Roystoneas are really fast even from seed and some heat will improve their growth. R. borinquiana seems to be the hardiest and IMHO much more beautiful than R. regia.
Another palm for you to consider is Clinostigma savorianum from the Bonin Islands Japan. It too is the hardiest of the genus and native to some islands that are very far from other Clinostigmas. I think some of these island species are hardy to cool and even some frost as they could not migrate with the Ice Age. They and their competitors had no where to go and all had to adapt or die.
Others to consider Sabal burmudiana, Livistona chinensis esp. var. subglobosa, Genoma undata. I'd think you'd be successful with many near cloud forest palms from the northern Andes.