I recently moved from a 6 Plus to an 8 Plus and am so so happy that I did. I was considering putting a new battery in the 6 Plus and trying to get another year out of it, but the sluggishness and reloads were really starting to get to me.
I forgot what it was like to have a new phone until I got the 8 Plus. Everything is smooth and instantaneous. I now see why some people upgrade every year lol. I really couldn’t be happier. My plan was to trade the 8 Plus in next year for an X Plus, but I am so happy with it I am thinking about keeping it longer. It really depends what Apple comes out with next year.