ej, either bullet will be a FINE selection for an all-purpose big game pill. Personally I would stick with the 180, there wont be 2"-3" difference in it vs the 165 at 400yds. Penetration will be maximized by the heavier bullet, but again we ARE talking about Barnes' so if you want the 165 then go ahead, they will still out penetrate other 180s like Nosler Partitions, Accubonds etc...

Good luck,
RA