i imagine that dpr will soon have actual photos from their test scene posted for eval, it's probably not going to be any big surprise, over what's available on the a7r, d800/d810, etc.
see the shadow recovery comparison here, a7r vs. 5dmkiii:
Sony A7R teams up with Canon glass
since the 5ds/5dsr sensor isn't much better than the 5dmkiii sensor, in terms of latitude, you can probably expect the k-1 to crush it just like the a7r did in the comparison above.
this is my a7r at iso10,000, horrible ambient lighting and a viv28/2.0 at f/2.8, no flash, imho the k-1 will be at least this clean, if not better, since it's based on the d810 sensor(??).