I haven't done any specific comparison tests, but in 4K mode, its pretty bad. I really like this camera, but the rolling shutter is a factor to take in consideration. If you're going to do handheld I have to say that the results I got with any lens without optical image stabilization are unacceptable. With the OIS Lumix lenses, I have been getting great results though.
Posted this in the main thread but figured I'd share here too in case anyone actually wanted to take a look. I made some clips this morning with the GH4. Did it in all pertinent modes and framerates (doh, I forgot to do variable frame rate 96fps, I'll try to upload that later). http://www.ecf.org/wp-content/upload...s/103_PANA.zip
C4K 24p
UHD 24p, 23.97, 29.97
1080p 24p, 23.93, 29.97, 59.94
Here are the results: GH4 1080p: 13.7 ms (13.7-13.5-13.1-14.0-13.9-13.5-13.5-13.9)
GH4 4K/UHD: 22.5 ms (23.2-22.3-22.7-22.7-22.4-21.8-22.4-22.8-22.6)
More details and comparison with other cameras in the main thread. Basically, fps doesn't matter, it is the fastest DSLR in 1080p mode (even better than some pro video cameras), and it is in the middle of the pack in 4K mode (between the 5D2 and the 5D3, for example).
One thing that this test told me: in 1080p, the GH4 only reads every other line (reads two, skips two, reads two, skips two, etc).
4K reads 2160 lines and has a readout time of 22.5 ms, 1080p reads 1296 lines (2592/2) and has a readout time of 13.7 ms, which is approximately 22.5*1296/2160.