I am guessing that demand for the iPhone X will not be as strong as Apple would like, given the pricing tier. However, if carriers offer good deals to suck people into their web of contracts, that could help weak sales.
I think the iPhone 8 and iPhone 8 Plus will sell strong. A lot of people due for upgrades. There are also people who have been sitting on the sideline watching the production quality of the7s, which I think will make for strong sales for the 8s.