Penny Morgan wrote:

Yes, they do get over 50 ft. In fact, I have a catalog from a local nursery
where I buy perennials, trees and groundcovers, that says they
eventually will get 60-70 ft. tall.

Here's a reference for you. My neighbor planted a row of them about 2 feet
apart (way too close) about 7 years ago. They were in 1 gallon pots and
were about knee high (little saplings). They are now about 20' tall and
have formed a solid wall. She has to trim out some branches once in
awhile and her husband tried to cut a straight line on the tops, but
couldn't reach all of them.

Close planting should keep them from growing to full height. BTW, don't
sweat not being able to reach the tops, since topping is a no-no.