Here's an update on my sweetheart, hopefully before autumn I will be able to taste the fruit for the first time. The cooler weather (65° to 80°) does not seem to affect it and would rate the cold tolerance of this plant at number one compared to the other bananas that I grow.
Cold Tolerance
1- FHIA-3 Sweetheart
2- Namwah
3- Raja Puri
4- Manzano
5- Gran Nain - Rose - Dwarf Cavendish - Veinte Cohol