A cold hardiness temperature indicates the approximate temperature at which the bamboo root dies in the ground. Typically you will get defoliation and culm death even before you hit that temperature. If Phyllostachys vivax can survive in your Zone, it will not put up 70' culms. I live in Zone 8 where vivax stays green all year long, and the tallest I have seen it is 40'+.

It is also not a good choice for you because it is one of the thinnest wall bamboos and the culms will snap in half under any significant snow loading.

If you want to try bamboo, I suggest you try something more cold hardy, like Phyllostachys nuda. It is hardy to about -20F, although that does not mean you won't have aboveground damage in the winter.

All Phyllostachys are runners, but some of mine have stayed fairly tightly spaced and others want to spread out more.

Thanks that's a big help! Especially the snow fall part... I didn't think about that.

How about green groove? I have fallen in love with that. It's good down to -10* and I don't know that I have ever seen it get cooler than that here.

I've looked into Nuda and it's just so boring. I was really hoping to go with something more fun.

Rosebud-
What are your expectations? Do you want a bamboo that is evergreen or are you ok with the leaves dropping and the culms possibly dying each year? Your Zone is somewhat marginal for bamboo, so you may have to make a compromise between what you want and what you can get.

We're looking to make a privacy screen across the back. I am not too concerned if they drop their leaves in the winter. I am actually quite surprised to hear that you don't think that yellow/green groove would do good here. I have read several people who keep them in Indiana in area that get more snow and colder than we do here.

I Live in SW Michigan and just recently found a grove of Yellow Groove 10 min. from me. It is approaching 35' in height and 1 1/2" dia. The guy that keep an eye on the property said that it had been there for 20 years. So it is not out of the question in your zone to grow this and plenty of others. I have a guy sending me some Spectabilis right now, so I will let you know in the future how it does!!! I love that stuff! Checkout this web site. He is probably closer to your climate than I am.

needmorebamboo.com

I grow a few kinds of cold hardy runners that I use for a wind break here in Maryland but they do well farther north. I find aureosulcata(which you referred to as green groove)very satisfying tho I don't grow yellow groove but the more ornamental spectabilis and aureocaulis. Quick to size up, small but dense leaves and first to shoot in spring. Bisetti is another performer, a green bamboo not as ornamental as spectabilis or aureocaulis but a heavier shooter also with small dense leaves. Rubromarginata is a taller green culmed timber bamboo, medium size leaves also very dense leafed and shoots all summer for me as I water regularly. These all do best in full sun. Arrow or Japonica is large leafed and does better for me in partial shade. Leaves tend to fade in full sun and are much darker green with some shade. Shoots are close together appearing as a clump and is the least invasive and best behaved of the runners I grow. Hope this helps.