I ask the same questions. Portra 100T was discontinued because not enough people used it to make it viable. I don't really know why Superia 1600 isn't tungsten balanced. I can't imagine using that in daylight for anything but special effects. For that a 85B filter would work fine.
The 80A daylight to tungsten light converter uses more light because there is a relatively low amount of red light in daylight, so much of the other two has to be removed to get you to your proper color balance. It's 1 and 1/3 stops for a 80A or B I can't remember and 2/3 for an 85B. Supposedly the job of the 85B is easier.