FWIW I had stellar performance from launch day and no noticeable lag even on 11.2 until this morning:
-Face ID not nearly as reliable and smooth. still usually works but i have entered code as many times this am as 11/3-12-6, I swear.
-Screen opened this morning to home screen, then went totally black for 1-2 seconds, then homescreen again.
-since then, periodic lag/freeze when scrolling or when swiping up and away on notification drops when doung something else on screen.
-and a couple of “what just happened?” moments with a drop or jitter that happened so fast I can’t describe.
I have done a hard restart as of 20 minutes ago and can’t say problems since. Transitioning to A1865 and Verizon IUP soon so new phone to come anyway.
Update: 7 pm. no lag on new A1865. On AT&T until tomorrow’s Verizon changeover.