I went ahead and pulled the trigger on an M 50 1.4. It was really a combination of features and price. I should have specified in my initial post that I plan to use the lens for narrative work, as well as interviews. I've just finished my masters in film production, and I am interested in using the lens on professional projects. In fact, I could have used it on a gig I was on last week, when the cinematographer didn't have one!
In my case, shallow depth of field is more important than macro focus capabilities, as I own a set of auto extension tubes, which are wonderful. Here is a link to my thesis film project, if anyone is interested. We shot the majority of it on a RED One, but there are a few shots we did with a 7D, and there are even a few car-mount for which we used my Pentax lenses.