Replying to Yet another ski length question...

Im 5'7 about 160lbs...23 yrs old, so not planning on growing any time soon!
Getting Line Anthems and trying to decide on 171 or 178?
70% park 30% all mountain

171 = eyebrow height
178 = just a bit taller than the top of my head

Ive ordered the 171's at the moment because this will be my first full season and i want to progress quickly and be more playful with my ski's...but i can change length if im quick

Suggestions please...