I've never grown S. gigantea, but based upon what I've read, you wouldn't get 10' out of it in zone 5, if it survives your winters at all. Resources vary on hardiness, with some saying zone 5 and some zone 7. If it's hardy to zone 5, it won't reach its maximum potential height in zone 5.

I'd go for Sacharrum ravennae.

I tried Stipa gigantea a couple of times in my former zone 5 garden. Even on sand I had no luck overwintering. I really doubt you would get 10' plumes from it anyway ...

Two other choices not quite so tall but with relatively small bases; Calamagrostis 'Karl Foerster' - shorter but excellent because it puts on its blooms early in the summer. Or, one of the tall Molinias will give you a look most similar to the Stipa. Molinia arundinacea 'Skyracer' or 'Windspiel' are quite nice.
A.