I fitted an older Black Scale varsity jacket the other day and a L fitted like a M to me. But mega said that the new cut & sewn pieces are all true to size so a Medium varsity (such as the hubert pentagram jacket) isn't gonna be way too tight? Thinking of ordering one, but gotta know for sure.
From my own experience, you should still size up. Other people do things differently though dependent on how they like their fit. I wear a M in tees, but usually a L in any Cut & Sewn stuff since it's very fitted. Some items are a little different and you should always try something on before you buy if you can.