You shoudl definitely be riding a 160. As snowolf said, NS boards have a longer effective edge than similarly sized boards from other brands. For instance my Heritage 158 has more effective edge than a Nitro TG 159 that I used to have.
18 Snoplanks Asym Fish . 18 Arbor Terrapin . 17 NS Maverix . 17 NS Twenty Five . 16 NS Swift - 14 TJ Brand Retro Fish
18 Rome Katana . 17 Burton Malavita Wing . 16 Burton Genesis X
16 Flow Talon