My vote would be to hold off on the BMC for now. It's a camera made by people who love digital cinema technology but completely forgot about the shooter. I shot a review with it and realized the only reason I would ever consider it would be strictly for in-studio use only.
Here's why:
- Internal battery: Are you kidding? This is completely impractical when shooting in the field. That's another grand right off the bat for an external AC/Anton Bauer or similar battery mount.
- Ergonomics: You take it out of the box, set in on a flat table, and it falls over forward... The awkward angle of the design isn't really ideal for handheld use without an additional rig. (not that DSLR's are much better, but they still fit in your hand much better)
- No HDMI: I had dreamt that perhaps you could use a thunderbolt to HDMI adapter, but no dice. SDI is of course the standard for professional applications, but for cheaper rigs and smaller onboard monitors it is harder to come by and much more expensive. This also means no ability to monitor/playback on a regular HDTV.
- Touch screen: Aside from the fact that it's almost completely invisible in direct sunlight, the UI is clunky and not practical. With no physical buttons, it takes dangerously longer to access and change iso/shutter/white balance/iris than on a DSLR.
- No overcranking: If you're shooting music videos, it is nice to at least have the option to do slo-mo. 60p on a DSLR isn't ideal, but it's better than nothing on the BMC.
- Unbalanced audio input: I assume the idea behind no XLR was to save space, but at this point it's pretty much equivalent to DSLR audio capabilities.
What the Blackmagic has going for it:
Better codec and data rate. The image is obviously going to be cleaner. Not extremely noticeable visually, but in post production that extra information can be crucial. Much better for effects and keying.
I don't think it gets anywhere near the 13 stops of dynamic range they claim it gets, however it is better than a DSLR.
Ultimately the BMC just isn't suited for high paced, run-and-gun style shooting, which most music video shoots for me are like. For in-studio or narrative use where you can set up and build each shot, it's pretty capable.
As some have noted, the lens choice is far more important than the camera, and this really can't be understated. I shot a music video on a 7D with some Zeiss ZE lenses and the footage looked way better than the RED Epic with old Nikon glass I was on the week before. Especially for music videos where you can get creative with lens choices, the quality and style of the optics is what defines the camera. (I suppose I'm not below the option to shamelessly self promote, so here's the link:
http://www.youtube.com/watch?v=I7bkbGTfYso Had some fader ND's so I could shoot the whole thing wide open at f/1.4)
As far as the overheating issues for DSLR's, I think it's pretty much moot. Any camera can overheat. I shot a concert with my 7D in the 100 degree Texas heat with no issues, and there are cinema cameras I've had overheat in warm rooms after light use. They are all electronics, and therefore will react to their environments in unpredictable ways... Unless you're going to be shooting for hours on end in the desert, I wouldn't make it a deciding factor.
Well that was long winded haha. Hope it helps. Both cameras will produce great images, but as a camera nerd myself I keep having to tell myself one thing - they are just tools and are only as good as the story you're telling!