My 2 cents:
On fz20:
Nikon 6T Max magnification factor = 1.3
Nikon 6T working distance = 0.33m
Nikon 5T Max magnification factor = 0.65
Nikon 5T working distance = 0.66m
The limiiation with Nikon 6T is that we often can't approach that closely to an object (such as a butterfly).