You could go for either the 161 or 171. Either would be fine. I would recommend the 171 as invaders are true centre mounted, very soft and symmetical so seem shorter. And a 171 isnt actually 171cm tall so it would probably be an inch(probably less) or so over your head.
^ yah but the invader isn't a race ski, it's a park ski, hense the butter zone, and i'd go short like the 161's cause it will make it easier to rotate on shorter skis