Become a MacRumors Supporter for $50/year with no ads, ability to filter front page stories, and private forums.
I regret installing it on my iPhone 6. Almost everything is slower. As kyjaotkb said, Messages is sluggish. If I haven't had it open in the last few minutes it can then take 4 to 6 seconds before the screen is anything other than white.
I think the OS is aggressively closing apps, not just sending them to sleep.
I'm waiting for 11.1, and am going to leave my iPad mini running iOS 10.

Not to mention bugs. Can anyone replicate this: Open Messages, swipe on the bottom app shelf until you get to the ... (more). Then try delete the Store app. Boom! Instant crash.
I would downgrade to iOS 10.3.3 while I still can, and upgrade once iOS 11 is faster and more stable.
 
Thanks to whoever put me onto this you tube channel:

iOS 11 is working fine on my 6 but feels slowish at times. Not enough to make me want to do something about it. That video suggests that the update will be faster. My iPad Air is much better after a deep nuke and pave. I might do the same with my iPhone 6.
 
Wife and I both have iphone 6 and have upgraded to 11. Ever since, battery has been an issue, Siri doesn't work and there's definite lag in opening/inputing/typing /etc

I'm sure there will be some improvements in upcoming releases for older iPhone 6 users, but those devices are seriously constrained by the 1GB RAM. iOS is now written to take advantage of devices that have 2GB and more. Unfortunately it is time for you to buy a new iPhone if you want a really great experience.
 
Register on MacRumors! This sidebar will go away, and you'll see fewer ads.