If i were you i would go for the 171's since you ride all mountain a lot. The extra length will be more stable and you won't out grow them so quickly. Also you'll still be able to rip them easy since its a pretty light ski
z12's are all plastic and not very sturdy. I would recommend a mount fairly close to center due to the chronic's symmetric flex (like center to -2 cm) A good binding would be sth 12 driver or sth2 13