Larger than #8 wire may allow higher charge rates, but in most installations still will not make much difference in charge time as you will not see those higher charge rates for long. Exceptions would be large, high acceptance rate batteries, e.g., 400 AH of AGM cells.
The typical 200 AH or so flooded battery bank will only take 50 amps or so, and not for that long before the acceptance rate falls off. The last couple of hours of charge is going to be 20, then 10, the 5 amps as the acceptance rate drops. Also even though alternators say 110 amps on them or whatever, the hot, continuous output is likely to be much less. And when they are generating 100 amps, they get very hot, very fast (automotive alternators are only about 60-70% efficient).
Even a high quality 200 AH AGM battery will only take about 100 amps at 50% SOC, in half an hour that will drop to 50 amps, in another half hour 10.
