K2s are not longer than advertised, they are as advertised. Other skis are shorter than advertised. K2 is one of the only, if not the only, company that measures skis the right way (after shaping them).
I am a little taller than you and about the same weight, maybe a little lighter, and I ride K2 Obsethed 179. I would go longer before shorter. If you are an aggressive expert skier then definitely get the 179s, if you are strong advanced probably the same thing. If you are a beginner-intermediate the 174s would be better.