As stated in the pattern preorder, size details are not final until the pattern is released and may be subject to change due to final improvements based on the testing and editing process. If in doubt between sizes, we recommend making the smaller of the two sizes and working a simple additional set of increases at the sleeve divide to get the additional ease/room that you need. (If you're a member of Knit Camp, we'll be chatting about this in more detail during the knitalong.)  Yardage estimates usually include a bit of a buffer to cover you if you need to make slight adjustments.