I was on the fence about x or 8+. I've had my 6+ since launch and it was really showing it's age and installing iOS 11 on it basically crippled it. After comparing the X and 8+ I pulled the trigger on the 8+. I love it! While it would be nice to have the edge to edge screen I just can't get behind the design choices Apple made with that notch. Also, all the UI compromises to make that screen happen really bugs me. Maybe next year when the product has matured a little I might reconsider.
Yeah iOS 11 was noticeably laggy on my 6s+ and the 6s+ is quite a bit faster than the 6+. 11.0.1 helped a little but it still was nowhere near as fast as 10.3.3. Can't imagine what iOS 11 would be like on a 6+. :/