umm im 5'9 140 pounds and i am rocking 178 invaders. You def should to, since there center mounted its gonna feel smaller, and since invaders are soo noodly to begin with your gonna want that extra length for jumps, even on 30ft jumps its gonna help. I am going from 161's invaders (last year) to 178's, the 161's were way way too short, so i def say 178, but 171's are fine to. Would be easier for rails.