I wear a Large in everything First Lite except for the Llano's, which I size up to XL. I don't have a vest but do have the 2nd generation Sawtooth Jacket in Large and it fits perfect as a second layer over my Llano. The guys that say it runs small are probably either referring to the 1st gen Sawtooth (before merino-x), which was a shit-show in the way it fit...or specifically the fit in the upper arms, which is snug but I quickly got used to it. It would be a struggle to put my Sawtooth over more than one layer though due to the tight arms and bunching of the layers under the Sawtooth. The Torso fits perfect so I don't think you will have any issue with a Medium vest.