I'd go with the 166. That's what my wife and I haul and storage our boards and a good amount of gear in. I ride a 160 and my wife rides a 156 and we put the extra bag space to good use. I've used the bag with only my board and I didn't need any other luggage--checked or carry on. It fit everything I needed for my 3day trip. If you are wanting to pack cloths/gear with your 157.5 into a board bag, then I would suggest this bag and size 166. I hope that helps.