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I'm 5'6" and ski 169 park skis and 188 powder skis (S7s).
There are so many variables when deciding what's best for you though so more info is essential: height, ski ability, type of terrain you'll mostly be skiing and how you ski it, whether the ski is rockered or not etc.
I was sceptical at first about getting the 188s over the 176s but I am so glad I did because I feel like i get best of both worlds - the rocker makes them nimble enough in the trees for me but the extra length gives me more stability on landings and at speed.
The best advice I can give to consider all the variables and which are the most important to you and then just go and have a decent chat with a ski shop you trust. Ideally demo some different designs at different lengths on the terrain you want to be skiing and see what you're most comfortable with.