kinda depends on what your doing. those all shoot very similar but extremely different. where do you feel limited when shooting?
the gh3 shoots 1080p at 60fps and the hack on those can increase the bit rate i hear quite a bit.
the bmcc shoots RAW 2.5k but only up to 30fps. and as well as ProRes at 1080p and has 13 stops of dynamic range which is only .5 stops less than a Red Epic not in HDRx mode!
both of those cameras are micro 4/3 mounts tho so the sensor is a lot smaller than a 5d and there is a crazy crop factor on both especially compared to a 5d.
so basically you gotta look at what you will be shooting and the type of look you want. the bmcc is awesome and looks super good and the gh3 is small light and also makes a great image.
the 5d is also a good camera tho too and can make some great images. so what do you want from your camera?
more dynamic range - bmcc
higher frame rates at higher resolution - gh3
just wanna spend money on a new camera - stick with the 5d and save up for upcoming models that will have exactly what you want