Hi Thane, I had used Hemlock stringers and treads for the stairs in my barn. Stringers were 4"x12", treads were 3" by 11". All rough sawn. Stairs have been up a couple of years now and there hasn't been significant shake. The treads are housed in the stringers which helps. The timbers used in the barn are Hemlock as well, shake hasn't been much of a problem.
I'm not a full time timberframer, I do it as a hobby. Built the "Sobon" shed and a 28' x 36' barn with a 12' x 36' shed addition. Have volunteered my services with other timberframers just to get practical experience. I've noticed that some timberframers are very negative about Hemlock while others use it exclusively. Not real sure why, perhaps one bad experience with it and you resign to never using it again?
Joe