For 720p shooting at 24fps, the Ultra cards should work perfectly well. For 1080p shooting at any frame rate and for high speed 720p shooting, you'll need the Extreme Pro write speed for best results in my opinion.
I think that entire interviews shot from a single angle - from a single, unvarying position - are difficult to follow. Your D7100 can work perfectly well if you stop every 5 minutes or so to change the shooting angle, check the lighting, take sip of water, work a bit with the interview subject, and so on.
Interviews, for entertainment or research or family genealogy purposes, need shot planning. Interviews for security or law enforcement purposes do not.
>It will be for family history and genealogy. >Would think 5 minutes is too limiting. Probably use my old >video camera.
The D7100 is rated for between 20-29 minutes of continous video shooting, depending on the resolution and quality settings. So my 5 minute suggestion was really more of a generalization about breaking up a long, boring, fixed shot angle. If you're doing genealogy interviews, you're probably good to go with your D7100. Just use an interview timer to give your camera a rest and avoid overheating. if that's not possible because you don't want to break the train of someone's thoughts - especially seniors - then your old digital video camera might be a better choice.
I think the choice of camera also might depend on the reason for gathering the interview footage in the first place. For example, if you're going to be using the footage to compile a documentary video about a family history, the higher quality D7110 footage might be the best way to go. On the other hand, if the footage is being gathered mainly for fact gathering in order to preserve family stories as well as genealogical history for compilation as a book, web site and/or family tree, the digital vidcam footage will do quite nicely I think.