I'm guessing that:
- you don't want to hide your lovely gate.
- you don't want anything that grows to wide for the space
- you would like something that would blend with your formal border with the LOVELY roses.
So ...
How about using one of the Calamagrositis arundinacea cultivars. Maybe 'Karl Foerster' or 'Avalanche' or .....
It looks fabulous planted in a group; it is narrow in growth form & it is still one of the best all season ornamental grasses out there.
Here is a planting of 'Karl Foerster' - picture taken this morning in my garden. This year, in bloom, it tops out around 5'4"

I would agree with "achnatherum". The upright nature of 'Karl Foerster' or 'Avalanche' or 'Overdam' would be ideal for the setting and give a formal look. If you want a privacy hedge, you could plant two rows and stagger the plants so that visually they form a barrier. There is a new Calamagrostis xacutiflora cultivar called 'Eldorado'. I haven't ordered any "yet" but have them on my list. It's touted to be "decidedly golden" and tolerant to zone 4.
Gej

Here is a link that might be useful: Grasses & Gargoyles

A related question: I have approximately 17 feet alongside a garage that faces North. Can anyone suggest types of ornamental grasses I should look for?