My dad has been growing musa basjoo up in East Lyme Connecticut and trust me it get's alot colder for a longer duration up there. All he does is pile on about a foot or so of mulch around the pups and main stem(s). The main stems die back but come back each year to a height of around 10 ft. There is no risk of losing a musa basjoo in Oregon, or northern California if one follows the same regimen.
Here is a pic from August of this year...
Banana Gallery - Musa Basjoo in East Lyme, Connecticut