I have mixed sun hemp and forage sorghum the past two years and they have been great screens. The sun hemp even doubles as food for deer. The deer can't eat it fast enough as it grows very fast and is not hampered by the browsing. Deer use the plot I screened exponentially more during daylight than they did prior to the screen. I planted miscanthus last spring to replace the hemp/sorghum screen as I won't have to replant every spring once it grows in. I believe, based on the growth I had last year with the miscanthus that its quite possible I won't have to plant it next spring.
This is also the first year I have seen pheasants on my property, They and quail use the screen for cover and food. It holds up well into the winter and still can't be seen through from 5' and lower. It is 12 to 15' wide.
When I used forage sorghum alone it fell over in strong winds and snow but with the hemp added it can't fall down very far as the hemp stalk is stout. I planted mine via broadcasting into disked ground and then dragged it via a harrow and then cultipacked it. I planted it mid to late May. I did't use any herbicide pre or post. It grows so fast it shades out the vast majority of competition.