I agree with the others about the 70D being useless since you have a GH4. It is also clear that the FF camera will best the APS-C camera in high ISO performance. The 6D is way better for portraits because it renders much smoother bokeh due to its FF sensor. The 85mm 1.4 will be a dream on that camera. I would definitely recommend to get the Eg-S Focus Screen for more accurate focusing. For sports, the 70D is much better, as it has a much more functional autofocus (the points are spread wider over the sensor and it has way more crosstype points) and more speed (frame rate, buffer...). But all in all, I think the 70D is the better compromise, as it can do portraits better than the 6D sports.
It's hard to read that my lovely 70d is "useless" but I get what you mean
If you're just considering your work and the GH-4 will cover all the video then for work alone the 6D seems a very clear choice though the 70d would do a job too I would say but depending on your lens collection you might have to make changes there too. The 6D will shine on those odd occasions where you might not have the full control and perfect lighting.
But if you're serious about Sports photography . . . and do try it you'll love it, it's just a whole different world of picture taking . . . then the 70d comes into its own.
In effect you've fallen down the same hole as many of us. We can only afford one camera (well in my case at least) but because our photographic needs are diverse there is no one perfect answer unless we want to spend the equivalent of two or three cameras worth of cash! Whatever you do don't listen to anyone who says that one is "better" than the other overall because it all depends on the value you put on the features that each of these excels at. I know I'd love to have both!