OK, I got my M crewneck yesterday and wore it today, so after a day's wearing (which may have stretched it out a bit, but if so, that would be more realistic):
Chest: 43" right at the armpits,
Back length: 27.75"
Arm length: 25" (top of the arm) 18.5 (bottom of arm)
I'm usually a 39 coat, between R and L and it fits me pretty much perfectly. It's trim but not tight. If I wanted to fold the sleeve cuffs, the arms'd be an inch short. But for this sweater, I like them flat. The weight is nice, I'd say just a bit lighter than mid-weight. Not a very dense weave, but dense enough. I found it very comfortable during all-day wear w/ just a t-shirt underneath. I'd be tempted to get them in multiple colors. I got the pearl gray and it's really nice, not quite as light as on my monitor, which I like.
thank you sir, just what i was looking for.