Looking only at the numbers, it's a 16% bigger battery (1560 mAh -> 1810 mAh) with a 18% bigger screen (4" -> 4.7"). Considering that the screen has an energy impact about 100x greater than the CPU, any energy savings in the CPU will hardly improve battery life.
So these napkin calculations say that the battery life will be 116/118 ~ 99% of what it was before. So we may see the slightest drop in battery life and Apple will ignore it and advertise it as having the exact same battery life as before.
Do you realize that your napkin calculation assumes that the screen power use would represent exactly 100% of the entire power consumption of the device?