Then the question becomes if spending an additional $400 is worth the marginal performance and battery life gains. The 6S+ is no slouch so holding it on for another year isn't bad at all.But you could have sold 6s+ to offset maybe half that or so?
For me, I'm on the fence between my 6S and 7. I'm leaning towards keeping the 7 because I love the color (matte black) and the haptics engine integration. I also got a great deal on it. Depending what offers I get for my 6S will probably be the deciding factor.