Summers@summers - I am about the same size as you. and I think the medium fits me perfectly. I can wear a base layer and light to mid weight base layer underneath. I would only advise you to size up if you plan to wear more layers underneath or if you just prefer loose fitting layers.
SummersThis jacket is not loosely cut and I don't think you would be swimming in a Large, especially if you expect to layer it much. I do have about ten pounds on you but I would not want a Medium except purely as a shell over a base layer. The Flashpoint is the best performing shell I've ever owned. And combined with a merino base, fleece pullover, and Ghost Whisperer puffy it has kept me warm down into the high teens.