A friend described it as being like an alarm clock.
Had hands on with c300, 11-16 lens is good on it. No money for anthing esoteric. L 2.8 zooms I'm afraid.
I tried the C100( many friend have them) is more handy and flexible than the C300. If you are doing video most of the time no need to consider 5D at all, it is a photo camera with manual video function and mono audio. Whereas C100 have flip screen, peek, zebra, S35 etc. good set of connectors. Also seem like the price of C100 is going down.
Since you are using 600D may be you can use 70D, performance is promising. especially if you are using EF-S lens.
As for BM4K I think the post production hardware requirement is a bit tough, BM4k may ok because it uses a relative common codec, I have great problem with the 1DC 4K files