Yea, i did the same and went back to 10.3.3 ASAP!
It was "slower" but not seriously slow. I tried an app load test and like i said above, they were down on load times etc but once loaded up, all seemed fine. Surprisingly, I found the control panel smooth to ues (?). Half of me wants to go to 11.0.0 but 10.3.3 seems to be about the limit now for iPhone 6 (non S) IMH.
Shouldn't apple put a disclaimer on the websites:
""""IPhone 6 and lower will benefit from all of the IOS 11.0 features of their more expensive counterparts, but will/may reduce performance so please be aware of this when updating"""""