85mm 1.4 is definitely a worthy lens for anyone who does portraits. Some things to consider about the Rokinon brand may be chromatic aberration and color rendering. Even on my high end 85mm f/1.2, chromatic aberration can be a major issue when using wider apertures depending on the lighting, and while it can sometimes be easily fixed in post with ACR or Lightroom (and I'm sure other softwares as well), sometimes it's so much that it can't be fixed without some editing done by hand in Photoshop.
I don't use the Pentax system, so take what I'm about to suggest with a grain of salt, but is your camera a newer one with a new mount? Last year I was able to acquire my dream lens (85mm f/1.2L II) because it has the previous Canon EF lens mount, making it significantly less expensive than it used to be. I use a camera with an EF mount so adapters aren't something I needed in order to use it, but perhaps an adapter for an older Pentax mount for an older Pentax 85mm lens could be a good option? From what I have been told, modern adapters don't reduce the image quality or lens performance. When I move up to a mirrorless camera I will definitely be keeping my EF 85mm f/1.2L II and getting an adapter for it instead of upgrading to the RF mount 85mm f/1.2. I love the lens and don't see a reason to replace it if I don't need to.