It's unfortunate that the sensor size isn't even twice that of full frame, I have to wonder what it is that makes the body so much bigger when the sensor is only 10mm taller?
What's the buffer depth in RAW?
Guess in detail that depends on the raw format used. Pentax's own? Or DNG? About 10 framis iirc.
Partially the body dimensions are a result of the lenses. At least the older ones are designed for good old chemical film. Which comes with a certain minimum depth for the mirror box.
Another reason is ergonomics. Despite the larger weight working with a MF is much less tiring thrn with something NEX/A7 sized.
I guess it's a nice product for what it is, but I still don't see it being 3x better than a 5D3/D800.
Those two are not the best comparison - with either the better viewfinder or zebras the MF wins, not because of the technical details, but for the ease of making actual use of them. If you want to take the guesswork ot of the equation the A7r would be the most fitting small frame counterpart.
But yes, at the moment it has a, in linear terms marginal, resolution advantage. The design feature that makes such a camera a no brainer for high end commercial photography is missing though.