Thank you very helpful. Sounds like the fit may be between your size and a size down, making it a pretty individual matter. We already have their Woolies and Pacifica (like Woolies but with no high neck for warmer use) L/S tops, S/S zip t's, a heavier winter L/S that's heavier than the Indie and a sweater. The fit on those is pretty consistent and true to our usual size, but I've never tried the Shak. Probably will order regular size and one size down to be sure, and report on what we found.
If the weight was a little over 8 oz on a medium, than I'm guessing the weight of the wool is just between Woolies and the heavier winter L/S top we have which I think weighs in around 12 ounces, which would give it a very wide comfort range, and perhaps often replace our current cool-cold base combo of a Patagonia R1 Hoody over an Ibex zip neck T (which works very well for us).