I have a miscanthus 'giganteus' that grow to about 9 feet. But it doesn't really spread. It should do great in your zone.

Lots of grasses will grow in your Zone. The problem with many of the really tall grasses is that they start to grow so late in the spring (they are warm season grasses) that the screening effect doesn't happen until July.

I do most of my research regarding grasses on the Bluestem Nursery website. They also sell willows, which grow really quickly. I suggest you investigate using them for a screen.

Here is a link that might be useful: Bluestem Nursery

Perhaps an evergreen would do a better job. Arborvatie may be a solution. Grasses take a while to become a "screen" and only do so for a relatively short time. Feather reed grass "Karl Foerster" grows seed heads the earliest, by June, but is only 5 feet or so even then. I love ornamental grasses but I doupt any will do what your looking for. How tall of a screen do you need?

Well-my old zone! If youare looking to screen out that lady THIS summer-nothing will do it like these two things-The first grows about eight feet a summer! I brought four pieces last year-in my little fist-a friend thought they were bamboo!-now-the tallest is nine feet-it's in back of the garden (good thing)-and it extendsabout thirty feet laterally and about four feet thick in some places! Yes-it's invasive-but-free!!!!!If you get to Florida you can have half!!! Or I can send you a bunch of rooted ones for postage.....It is called Arondo Donax. It is green-indestructable-and spreads.The spreading can be controlled by wood or metal planks sunk to root level to obstruct-or pot it in HUGE pots.The second is a pedt here but pretty-and grows about four feet a year-it is a tree called Brazilian Pepper-red berries at Xmas,and evergreen!Can be controlled and cut asa hedge-very invasive because of birds and dropping seeds by said birds...You can E mail me! ,,,,,M

Brazilian pepper is not that cold hardy.

How about Giant Chinese Silver Grass?