Wire charts are always conservative. Meaning if the wire is rated at 100 amps, it will easily tolerate 100 amps forever.
Now, wire is not always rated at its gauge.
That said the wire should never be maxed out continuously.
They say #4 is good for 100 amps because on paper it is. Would I personally rely on one #4 line for 100 amps of continuous power? No.
Would I use two 4ga lines per pole and 50 amp fuses on each line? Yes.
This would stay below the wire ratings.
2ga would be better. The cost difference is small so use 2ga if you can.