Replying to Backcountry "Expert" Recommendation

I'm about 5'7", 130lbs. I ski probably 30% park, 40% trees, 30% groomed. I am currently on 155's, I know, way too small for me right now. I can 7 on the 155's, but I want a longer ski. I bought 3 years ago when I was a lot shorter and lighter Anyway, I want to buy some Rossi S3's, and the guy at backcountry recommended 160cm for me. I was thinking more 170cm for me. I live in the Midwest, but I get out west about once a year and I ski Mount Bohemia every now and then, which is just as good as anywhere out west, in bounds that is. Any opinions on this? 160 or 170?