I originally bought the 6 plus back in the days, then ended up swapping it for the 6. I loved the screen of the plus, however weight and the one hand usage really got annoying. At gym, i couldnt have the plus in my pockets, so i always left it out. And few times i left it behind. Was nice to surf on, but sucked when i was in bed, was really awkward to hold with one hand and surf. And from the specs, looks like the 7 plus is even heavier than the 6 plus.
Also plus wouldnt fit in my car's cup holder, so i had it tucked under my leg. One of the things i missed when switching was the battery life, however the 7 seems to have increased the battery life so that should be very helpful for days use. And finally the OIS, made big difference in my photos from plus to 6. However with OIS in 7, that should really help with my photos.
Hard decision, i think both are great phones. Really depends on what your daily activities are. For example, taking a train everyday and want to catch up on a show, maybe plus is better suited. You use your phone daily for gym and like to use arm bad, maybe the 7 will be the better choice.