Having owned both now, I will say that I would have had trouble giving up screen size. The reachability feature truly keeps the Plus as a one handed device. I've used the feature several times today already. Plus the battery life on the Plus is sick.
I was talked out of the 6Plus phablet by friends, so I pre-ordered the 6 Space Gray 128 gig. I really like the 6 with OS 8. Slick interface, fast, easy to use. However, after having gone to the Apple Store Friday night and playing around with the 6Plus, I now regret downsizing. For what I want to do with a phone, I think the extra screen size will be fine. Yes, as a telephone it is huge! But I will be mostly using my phone as an internet device, like Jobs originally described the iPhone. I probably talk 200 minutes a month. The rest of the time I'm browsing, reading articles, email, and the like. Even when I talk, I'm not holding the phone to my ear, but using earbuds or a bluetooth device. Now that I have the 4.7, it is just too small to read articles on news sites. I still have to carry my iPad around at work too. I already ordered the 6Plus. I should have listened to my intuition in the first place.