Surface Upper sizing

Torn in between sizes, 168 or 176. I’m 5’6”, 140 ski primarily smaller hills on the east coast as well as carinthia, park like 90% of the time. Typically have skied 172s but looking for something wider. A lot of people I’ve talked to riding them have said they’ve sized down due to the wider width for park. Have been running into some knee issues so thinking the 168s for the maneuverability. Advice?