There are a few important things to point out here:

A 25% IMAC airplane is usually designed to fly on a 30cc gas engine. As such, everyone flying electric (and even some flying gas) ends up adding weight to the nose since a gas engine has all that mass concentrated just behind the spinner. Batteries are too far behind the firewall so don't think bigger packs will get you there. I will have to jump through hoops to remove weight from the tail of my 26% and will likely still need extra weight in the nose even with 10S 5000mah batteries. So if you get the Pilot, save yourself some cash and get a motor that's not optimized for the lightest possible weight. An A60 Hacker would work well, the E-Flite Power 160, etc.

The 78" Extra has an 'electric version' - I don't know what the difference is, but at least electric power was considered in the design so hopefully you don't have to add weight to the nose. But you will still benefit from a bigger motor to handle the increased heat (Hence the Neu 1515 as opposed to the F3A).

The Neu F3A is optimized for pattern flying where they tried to remove as much weight as possible. The F3A is in between a 1512 and a 1515. The 1515 is a little longer and a little heavier, and capable of handling a little more power. It might be less expensive too. Since you don't have the same weight requirement in IMAC you don't need these 'pattern specific' motors and less expensive motors might actually be a better choice.

Motors turn chemical energy into power and the waste product is heat. You need a specific amount of power to fly an airplane, therefore generating a fixed range of waste heat. A motor with more mass will not get as hot as a motor with less mass given the same heat input. Heat has the biggest impact on motor life span. There is a good reason motors get bigger and heavier as you go up in power rating.