You might know this, since you are thinking of getting the BPL UL Merino over the Smartwool Microweight, but the Smartwool microweight is the same 150 gram/m wool as the BPL Beartooth, vs the 115 gram/m of the UL Merino.
I have to say that I really like the way the UL merino manages sweat. It never gets heavy and feels clammy the way even the microweight stuff does. I really do find it to be my favorite baselayer when the temperatures allow it to be worn under something sturdier like a wind jacket. Which is pretty much every season but East of the Mississipi summers.
I actually wish BPL made their merino boxers out of the same weight of fabric. I have a pair of the 150 gram/m make I got in the big sale last year, and they just retain a lot of perspiration and get clammy in a region of the body that tends toward that. I wore the underwear and the UL merino hoody as baselayers all winter riding my bike 12-15 miles every morning in Central Park. The shorts went under powerstretch tights and the hoody went under a powerstretch jacket, and the difference is sweat management was drastic, in my experience.
When I 'put my thumb' through my hoody, I was taking it off after a morning run, and I was really sweaty, and since the fit is athletic(read: skintight), one has to be careful taking it off. I realized this and was just careless once. I've also ripped the collar seam on a golite drimove t shirt in the same situation.
My experience has been that the sweat management of the UL Merino is comparable to my Golite Drimove t-shirt, with the wool being my more soft against the skin and the polyester seeming a bit more durable.