After using it a while I am finding B6 pretty good really - battery life seems really good.
It still stutters here and there - most noticeably when a lot of graphics are moving around - so, the Mobile Data page in Settings, and scrolling through Emojis on the keyboard.
Safari also seems a little stuttery on some pages.
Scrolling Photos with the Photo info visible (IE, not "full screen"), has some micro stutter at the moment the Date changes as you are scrolling between Photos - most noticeable if you slowly scroll rather than flick.
Weirdly, my iPad Mini 1st Gen actually feels somewhat smoother in areas like Safari and Photos - for such an old device this is odd behaviour, so I can only put this down to Metal vs OpenGL.