i would say you want under a 1 volt drop, yea 3 % is electric code for houses and bussiness but as you have seen 3% on 12 system is hard to get. the lower drop you have the better, but it is a balancing act of too much weight vrs too much drop. this is why an led light is so great, it uses less so you can get away with smaller wire. i would play with the wire sizes to see where you get the best drop vrs the weight and find a middle ground.
btw this is also why you dont want to share neg wires on a boat, it can cuase too much drop when both things are on.
disclaimer i am a real sparky but not a boat one, so what i say may not be right