I would definitely look at the reviews of the XF-400 at B&H before purchasing this camera. It appears to have a great many functional drawbacks, many of which would deter me from buying it. Regarding your original question, you'll probably rarely if ever need the SDI connection for the kind of work you're describing.
For video editors, finding the perfect portable workstation is like catching a unicorn. It is no easy task to find the perfect balance of performance vs price point.
