As someone said a few pages back, "they're all S years now," as the improvements become more incremental. Your X should be fine for at least another year.... As we all know, this is a ‘S’ release, so we are likely to see a more substantial upgrade in 2019. The thing is, when go back to my usage pattern and the fact that Apple is finding less and less meaningful technology to get users to upgrade, I feel even more justified in changing my upgrade strategy.
The S years are the ones for me ... by now, most apps I care about should be updated for the new screen sizes, FaceID is more mature, and the no-button gestures have been embraced by most if not all. The 3GS, 4S, 5S, and 6S were my favorites ... I'm on an 8 now which is really a 7S. I'm eagerly awaiting my Xs now that things seem to have settled in. I intend to make it last at least thru the payment cycle, as replacing a $1300 phone every year seems like the sucker's choice, Apple enthusiast or not.