On the surface, this seems like a penny wise pound foolish discussion. The cost of wiring on your layout is actually one of the smallest expenses you will incur. To use wire smaller than #14 going to the track either full loops or to blocks is a savings one MTH 20- freight car, maybe. For the drops to the track I would use #16 or better but then I always over build. If you want to run #18 which I probably would not, run it to your Barrel Loader.
An electrician friend used the water hose analogy. The farther you go in order to get an equal amount of water you have to use a bigger hose. Electricity works pretty much the same way. The longer your layout is powered up and the more trains you are running the bigger the hose you need.
