Great report, really good to hear on the battery life. I have similar use case to you. Email, Office Suite, browsing, etc. Although I do want to do some light photo and video editing and beginner programming in near future. Question: What brightness did you have it at throughout the day?
I also moved from i5 256GB to i7 256GB and also agree that i5 is the sweet spot. Like you, the extra money meant very little to me and because of a particular deal I got, I paid only about $125 more so figured why not. Had just been promoted at work and won $5,000 in a contest in the same week. However, for anyone on a budget or just doesn't need to have the latest and greatest, and isn't doing intensive things, the i5 seems like the way to go.
Yes, I am also curious about the brightness used. I took a couple of courses last year and used the SP1 to take notes all day. The lowest brightness worked fine for me since I wasn't reading the notes at the time. I had no problems getting through the day with 35% battery left at the end.
I have a couple of more courses coming up this fall and I can't wait to bring the SP3 with me. So far, mine too has been rock solid.