What length ski should I buy if I weigh 175 lbs and ski mostly in the back country?

Tech Specs:

Lengths:

165cm, 175cm, 185cm, 195cm 

Cap Material:

Carbon Powerbands, Greenlight Core 

Base:

Omnitrak NoWax base 

Waxless:

Yes 

Dimensions:

109 / 78 / 95mm 

Camber:

Single camber 

Recommended Use:

Nordic touring, recreational touring, cross country skiing 

Manufacturer Warranty:

1 Year