Just to sprinkle some real-world feedback since I went from iPhone 6 Plus to the iPhone 7 Plus, the difference in speed is noticeable.
I carry both phones around with me (because I can) and when I use one then the other, the performance difference is noticeable right away. The iphone 7 is way smoother, launches faster and is almost lightning fast. The only negative for me is the iPhone 7 Plus is actually slightly heavier than the iPhone 6 Plus.
Both are 128 GB models and they are both being used without screen protection or clunky cases. Apples to apples comparisons.