Well,
You've done the work so this might not sit well:
When all the religion and my dad said and 6volt 1940's cars are taken out of the factual pile:
Pound for pound they're identical those 6 and 12's.
The sixes allow you to divide the size... And that's all.
Been there and done that.
I Have twelve of the 6's sitting here awaiting a project (half of them are powering the greenhouse... Had to use them for something)
Free is a very very strong reasoning.