Don't waste anymore money on synthetic baselayers. Merino wool is where its at. I had been wearing a UA coldgear mock shirt as a baselayer, it was heavy, always rode up and smelled like hell after a long hike. This stoic merino shirt is the bomb, its light, enough to keep you warm on cool days (~50F with wind today) but light enough to wear alone on warmer days to keep cool. layered under a windproof shell, it might be all you need. its lightweight and perfect for my kind of hiking and running. I'm 6'and 150lbs and the medium fits well.
Bottom line: toss your synthetics, pick up this merino, you wont regret it.