I have had the 15" TB for nearly a week now, and am considering returning it and getting a non-TB 13".
First of all, battery life is AWFUL. And before anyone says anything, I don't game/video edit, I have let spotlight finish indexing, I don't run Chrome, brightness isn't max, and I've reset SMC. I'm getting about 4-6hrs on average, just browsing Safari, occasional YouTube watching, and typing in Excel and Word. This is such a disappointment...most of why I decided to get the bigger screen was thinking I would also get better battery life.
Don't even get me started on the uselessness of the Touchbar. I haven't once found that it increased my productivity, and if anything I find myself accidentally resting my left hand on the Esc key and exiting fullscreen mode. The need to carefully hunt for the exact place to tap your finger on it to perform a function completely negates any time savings you would get over just moving the mouse to the appropriate menu option. Furthermore, it is a joke to have to look down at the keyboard to adjust volume.
In deciding which CPU to get, what would the difference be between the i5 and i7? Specifically, would one or the other make a big impact on battery life? Is the performance increase worth it, if I'm never really doing anything resource-intensive?