The Sony FS_00 cameras are fantastic spec wise. FullHD 50p, 240 FPS on the 700, metabones speedbooster giving you faster, full frame coverage. Blackmagics are great for final image output, raw and (at some point) 4k.
What they don't give you however is the functionality. All of my work relies on working quickly and creatively. I use the FS100 ALOT, and even after knowing the camera backwards you simply can't operate it half as quickly.
I did a speed test of the 5D mark iii and FS100 at a live event. I exposed for the stage (lecturn shot, high lit) and timed how long it took me to re-adjust both cameras to get a crowd reaction. Can't remember the timings exactly but the FS100 took nearly 10 times longer. I can operate a C_00 just as quick as a Canon DSLR now, they're that intuitive.
Relatively speaking speed of operation beats any spec list for the work I do. So for these reasons it ruled out any Blackmagic or Sony camera.
That left the consideration of the C100 or the C300. I wanted a better camera in-house, one that could replace my 5D mark iii as my main video camera, with decent audio.
What I didn't want it to do was cost so much that I'd try and sell it on every job I take on just to pay it off, meaning I'd pick it over a hire of a camera better suited to that specific job.
So for this the C100 made much more sense, I bought it outright and I won't feel bad if I need to hire in a better camera when required.
And when you actually compare them, over twice as much for the C300 is overpriced. The codec and viewfinder are much better, but not over twice as good. With a recorder for the C100 you can close this gap considerably.