I just psychologically would feel better with the i7. lol I know there is not a noticeable difference but I'd just feel better with the i7. My other laptop is an XPS 13 and it has a 6th gen i7 like the MBP and since my macbook pro is becoming my main dev machine I don't want my XPS to be more powerful than it, even if it's 5-10%
Another reason I want to swap out is for the color. I got space gray and it's pretty much the same exact color as my XPS 13 so I was going to go with Silver to have something different to use (I've never owned a MBP so it's not like the silver will feel old to me) and decided if I was going to do that then I'd also go with the i7.