zone 6 I think, but over all sikkimensis is a nicer looking plant. Where has M.basjoo survived zone 5 without any protection, that's kinda hard to believe?!

On the University of Missouri campus in Columbia Missouri there is a stand of Basjoo along a north-facing wall, at the intersection of College Avenue and University Avenue. I've spoken to the groundskeepers and they've told me that they do nothing to protect the rootstocks in the winter, and I've looked at the patch in the winter, they never pile mulch or anything. Every year they come back...it weirds me out a bit considering it's along a NORTH wall-I would think that it would be far too cold along a north wall to grow tropicals, but it seems to be working!

Mu8sa sikkimensis (IMHO) is a far more attractive plant than basjoo, but in a cold zone like 6 is much more prone to rot in winter than basjoo. I have luck overwintering basjoo, but sikkis rot in the ground no matter how I protect them.

I put Musa Basjoo and Musa Sikkimensis in Spring 2010, I know I am responding to an old post, but it is still valid.

Last winter my lowest overnight temp was 10F/ -12C and my Sikkimensis and Basjoos survived with no problem.
Both types wer protected with a bamboo pole / plastic sheet teepees which were filled with leaves.
I even managed to save about 4 feet of stem on the sikki by filling the teepee up to that point with leaves.

So, yes, at least in my experience, Sikkimensis is as good or better than Basjoo. I have a feeling they could have been left mostly unprotected and they would have come back from the ground, I just wanted to have as much a head start the following year as possible.