In my opinion, trying to find useful Frigate / Destroyer descriptions is pointless because every navy builds and uses ships differently. For instance, Japan's "destroyers" are single-purpose ASW ships, while India's "frigates" are fast multi-role ships. And that doesn't even get into the problem of ships that have been reclassified (e.g. Ticonderoga-class DDG) or are called different things in different languages (e.g. Horizon-class "frigates" with "D" hull numbers).
I think the only really viable classification method would be based on combat systems, much like how the old DD/CL/CA/BB designations were based on main gun size. However, given all the possible permutations, I have yet to figure out a way of doing so that is both accurate and succinct. So I tend to default to 75-100 meters overall length = corvette, 100-150m = frigate, 150-200m = destroyer, >200m = cruiser.