**** fast & unscientific ****
I had possession of a C100 & Ninja for an assignment for a few days, so right at the end I did a quick comparison of it's video quality vs my Nikon D800. I've seen plenty of C100 vs 5dMkIII comparisons, but none against a Nikon. This was done very quickly so please don't consider this an actual 'real' comparison video.
I mounted the D800 on top of the C100 via mini ballhead, which shows some instability with wind movement. I also only had a single Ninja, so I used it on the C100, which probably doesn't mean much since I was at very low ISO's with both and didn't push the files in post.
I was using the 24-105 f/4 on the C100 and the Nikon 24-70 f/2.8 on the D800.
In Premiere I applied very slight levels and color adjustments to each to make them relatively close in color and tone; yes of course this could be much more carefully done, but this is just a 'for fun' curiosity comparison.
I wouldn't give up my D800 for stills anytime soon, but wow was the C100 a pleasure to use for video. The experience has resulted with me being very dissatisfied with my D800 video, which previously I was quite happy with!