I found this text on where wild Musa grow in their native regions.
A few interesting things are that Musa Basjoo is actually also(besides Japan) native to Sichuan, China.
Musa sikkimensis is native to regions from India, China, and parts of Thailand(and places in between. So depending on where your seed is collected determines it's hardiness.
Musa itinerans is another wide spread species(from Xizang Zizhiqu(Tibet), all the way to Northern Veitnam, and parts of Thailand. But I presume that most of the seed collected, and the tissue culture(plant sold here) in cultivation is from the original introduction in Yunnan, China(at 10,000 feet).
There is also some other good info on other species from various countries.
http://www.inibap.org/publications/wildspecies.pdf