When actually seen in use a 4.7" screen is larger than it seems. I went to an ATT store and compared my 5s to smartphones with 4.7" and 5.5" screens. I saw that the font size on a normal screen was significantly larger than on my 5s. Enough so that I went with a iPhone 6.
The entire phone is larger than a 5s, and the 6+ is way larger. You may also want to consider how your going to carry it. It seems like a silly question, but all those who have grown used to carrying their phone in their front pocket are going to have to may a serious life and fashion decision and change. And this is with either phone, but especially the 6+.