I guess another deciding factor will be how long your interviews will be. The 7D is limited to approximately 12 minutes before it stops recording. As for DOF, you can get the required DOF with lens choice and several different lenses can cost much less than an adaptor, it will also cut down on prep time, extra glass between the lens and CMOS, will be a lot lighter, easier to transport, less invasive, large CMOS, better low light etc. Also, the sound issues aren’t a concern as you can plug a mic into this camera. I could be bias because I own one and I have just ordered my second one as am way impressed by this glorious box of goodness.
You could always use it as a second cam??? 🙂
Will be interested to know which way you go.