Technically, 8 would be fine on a 12V for only 16'. However, the cost difference in the 6 is insignificant if you had to tear it out and redo for 24V later. Go with the 6.
Wannabe...
Not trying to start anything here. But Ohms law says the greater the voltage, the less the amps on the same load. So that means if 8 works on 12vdc it will also work for 24vdc unless you change the load.
Alan
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Tight Lines to all Roll Tide Roll
Not trying to start anything here. But Ohms law says the greater the voltage, the less the amps on the same load. So that means if 8 works on 12vdc it will also work for 24vdc unless you change the load.
Don't have the time to get into motor formulas, but go look at any multi-voltage motor face plate and you will see the higher the voltage the lower the amps.
Alan
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Tight Lines to all Roll Tide Roll