5'7" in centimeters is 170.18. If you like shorter skis, Don't go lower than 168 cm. You can really go as long as you want. I don't know what size of skis you have shredded before but longer twigs are really fun. I'm 5'10 and ill be skiing on 181 cm planks this year. In my own experience people really only ski shorter skis because 1. They have no experience with longer skis  2.  They aren't good enough to handle long skis. 3.  A combination of the two.
If you ski powder. Go at least 176. Park is up to you but 171 cm should be the g-spot.