I have used a Windblock fleece vest for the last several years in similar temps up here in AK (mine is made by marmot, but almost every company makes some version). I have found I don't usually need a long sleeved mid layer, as the vest keeps my core toasty while still maintaining the ability to zip up or down if I am too hot or too cold. When I actually stop to rest or glass I almost always put on my "puffy jacket" aka insulation layer anyway, so I haven't really missed the sleeves. Really cuts the breeze when I am hiking, and when I slow down it adds another layer of warmth inside my insulation layer (Integral Designs Rundle jacket). I recently acquired a Sitka Kelvin vest, so I may give that a spin this season.