For all the same reasons Steve has listed (and I do love my K-01), the Pentax products are a generation or two behind where they should be for video.
I'd actually not recommend the GH-4, for my personal preference, and recommend an a Sony A7s with a K-to-E-mount adaptor.
I've used both GH-4 and A7s, and found the crop in the GH-4 to be very limiting compared to the full-frame A7s, and the menu layout on the GH-4 is pretty terrible IMHO.
The A7s is also the king of low light / available light shooting for video, easily as good as the FS700, which kicks the but of every Canon and most of the Reds.
Yes, the A7s is a lot more pricey then the GH-4, but it's a better camera for video, and it's stills match the K-5, K-01, K-30 for sharpness and detail.
The six most recent videos on this youtube channel were shot with a combination of A7s as the main camera, and K-01 or FS700 as the b-cam, with the Hit Training and Anzac Biscuit episodes also having a BMD 4K used.
For comparison, the 5 tips for Xmas episode was shot on K-01 and JVC GY-HD7, the JVC being a small, 3CCD camcorder, one of the very first generation of prosumer HD cameras, recording to internal HDD.
https://www.youtube.com/channel/UCakdn-ttH-r5aKo_PQDvRvw/videos?live_view=500&flow=list&view=0&sort=dd