The EV spread simply maximizes Attack and Speed for Golem. The Speed is necessary to outspeed every foe up to uninvested base 70 speed Pokémon. Adamant is the nature of choice because it allows Golem to hit as hard as possible with the Choice Band. However, Jolly nature can be another option to outspeed foes that speed creep Adamant Golem such as Pelipper and Mawile.