Well my 6 is a touch laggy
When in the messages app it takes three or four seconds for message details to appear on the screen when selected compared to instantaneously on 8.3.
Candy Crush, on 8.3 chain reactions of similar colours were immediate, now you see the colours freeze for maybe half a second before exploding.
I've cleared all suspended apps, done the hard reset and checked the available memory (a shade over 32gb free).
Short of deleting everything off the phone and doing a factory reset i can't see what else I could do.
The phone, while not unusable, is not pleasant to use at the moment.
I'm torn between making a backup and going down the hard reset route and hoping that na update fixes the performance issues.