Should I be selecting Accurate, Inaccurate, or Secure in the “Gap Detection Accuracy” box?

Accurate Accuracy should be quite good for any CD. If there is a problem CD, where the gap detection hangs, try inaccurate, as it will go on, when no information could be gathered in a time. If you got gap length that are wrong only by some blocks, you could try to do gap detection again with secure settings.