You can get an idea of the time to recharge your pair of 6s from this ugly graph. This also lets you decide what is "worth it" for getting more amps of charging in terms of cost of the charger, enough generator to run the charger, and the time it takes.
The key thing is the diminishing returns in time saved as you go higher in charging amps. EG useful in deciding if you would be better off with an 80 amper instead of a 60 amper on a pair of 6s compared with on four sixes.
Note- at the same amps, double the battery doubles the time, but on the same battery size, doubling the amps does not halve the time.
