I don't kno what you mean by mild but if it runs on pump gas with a full exh system (street car)and no overheating issues then I would probably just run a stock 360 plug. Colder plugs foul easier so if it's not needed then why bother ???
If this is a race only car go ahead and try a colder plug. some like to tune for different tracks /track conditions by changing plugs & adjusting timing.
It"s your call, really