I know I am a bit south of you, 7a/b, but I have great success with Basjoo. I have had them in my yard for 4 full summers and they are really doing a good job. I retain a foot or two of pstem over winter and have acheived 20' of overall height for the past two summers. All I have done is kept them mulched (year round) with 3-4" of mulch. I think a plastic bag-o-leaves placed over the pstem would be all you would need for most winters in a Z6. Here a pic of one of my clumps from this past summer... COME ON SPRINGTIME!!!!
I am personally 6'4" for scale...
