HI, I am about to buy the Rossi Scimitar but cant decide on which size I should buy. I am 175 cm high, 16 years old, and 80kg. I am a strong level 7 and quite agressive. I like going fast (almost straigtline) in groomers but doing short quick turns off piste. I have to chose between a 171 and a 178. Never used skis which were even near my height.