Atomic REX...how short to go?

Looking at the R:EX and BD Crossbow for a new AT ski. I'm 5'8 165, good skier, but am used to soft skis (1080s 171, Jak BCs 170); moving to a stiffer ski for more versatility in the east for on/off-piste.

Lots of people tell me the REX should be skied short - meaning a 168. Is that too short? I'm a little hesitant to go 177 due to the stiffness reported in the REX. It'll mainly be used offpiste in the east - tight trees and chutes (Tucks) while also serving as my onpiste ski.

Any input on length for the R:EX?

the 171 1080 is a twin and have a contact lenght of a 165, plus it is soft so go the 168 REX. It still ski MUCH bigger then the 1080 for many reasons