A few things: The NS dealers have largely sold out. Everyone has trouble getting boards now.
Here's a link
with a better chart but don't just look at charts - read the second part of the link that explains all the reasons charts are only rough guesses.
If you ride only groom and park, you can always go shorter. If you ride deep powder, you can go longer (especially for Japan). But, if you ride deep powder and trees, you need to go shorter and longer...er, I'm so confused.
If you go with NS, you can add something else to the equation - Rocker and Camber. By using both, you get better edge control and you can ride a little bit shorter. I love Never Summer stuff - great company! They have new stuff coming out in our fall (sorry). You might want to wait? You'll have an easier time of it and get to grab some incredible technology too. You know that sooner or later you're coming up to Niseko (Hokkaido). It's a rite of passage.