I am a more is better person when it comes to wiring. Within reason of course. In my case my trolling motor is within reach of my battery. At one time I used a small stern mount motor so I ran #8 wire from battery towards the bow to the stern. it ran my trolling motor and my depth finder. My boat is a 14 footer so the wire is only about 12 feet in length or so. Having a little tinny and a 9.9 outboard I take any weight into consideration, plus I already had the wire so no extra cost was involved. lol
I am including a link here that may help you.
Voltage Drop Calculator - Inch Calculator
knowing your full load amps is very important.