Actually, the leafless BOP, Strelitzia juncea, is THE most cold hardy of the BOP's. It can take to 25F. But its very difficult to source, places that get it sell out almost immediately and its expensive.
Strelitzia reginae in the orange form does not get more than about 4 ft. When I lived in Los Angeles in the 1980's, it was like the state flower almost LOL. Almost every yard had one, and they were constantly in bloom. The Mandela's Gold is like the orange, just yellow, so it will have the same size
