I was in REI yesterday and I saw they had the Smartwool midweight zip-T in stock, so I tried it on im my usual size M, and ... yikes !

That fit of that top is so much different than the fit of the microweight crew neck (which I happened to be wearing at the time).

The midweight top is a much snugger fit, and I looked like a purple sausage in it. I didn't bother trying on the size L, but maybe I will next time I wander thru an REI.

But it looks like I'll be sticking with my beloved microweight Smartwool.