It's different insulation but more of it. The 2017 Sitka does not have a wind stop outer. Weather has been such that I have limited use of mine in any wind. If you want warm and wind stop the 2018 Sitka will do that. From what I have read, the new first lite puffy is warmest of all.
Sitka makes a Kelvin Down Wind stopper Hoody. It has Gore wind stopper in it so it's meant for glassing in snowstorms and on top of mountains. They also make Gortex gear in 3xl as well as pants.