FYI: when you increase the solute concentration inside the leaves (ie. feed them high P,K a few weeks before it goes below 70F), some varieties can get frost on their leaves with no damage, but this is very dependent upon how long the leaves are exposed to frost. Other varieties, it seems no matter what, they'll turn brown with frost on the leaves.
During some years, I've had some bananas (ie. American Goldfinger) under cold, wet weather that never got frost on the leaves, yet a large amount of the leaf mass did eventually turn brown. It took perhaps 2 months of nonstop cold rain before it started getting messed up. Good example:
And here's what they looked like before the winter: