I am 5'8 and 150lbs. If I wanted to wear...
I am 5'8 and 150lbs. If I wanted to wear this jacket over a fleece for colder weather and still want a "tailored" fit (not feeling like the jacket is so big it's sagging or the jacket is so small it's about to rip), should I aim for medium or small?
Go for a Medium. I'm around the same size (5'8, 155) and it has enough room for a couple of layers. I wear it with my Marmot tempo and I can definitely fit another layer without it feeling too loose (I've also worn it with just a long sleeve t).