I stole a little time at lunch to compare camera resolutions.  Note: I simply took quoted resolutions at specified 
distances from public websites and normalized resolutions to 1,000 km distance.  View these as approximations.

So with that, here is how the high resolution/narrow angle cameras from various missions would compare at set distances:

                      1K km      10K km     Ganeymede to:  Jupiter    Io (closest)  Io (furthest)   Web quoted resolution

JSO                   2 m         20 m                     2.1 km     1.3 km        3.0km           0.4 m at 200 km
EE                   10 m        100 m                    10.7 km     6.5 km       14.9 km          1   m at 100 km
Cassini              6 m          60 m                     6.4 km     3.9 km        8.9 km          0.024 m at 4 km
MRO                  1 m          10 m                     1.1 km     0.6 km        1.5 km          0.3 m at 300 km
Deep Impact          3 m          30 m                     3.1 km     1.9 km        4.3 km          2   m  at 700 km

Page 3-5 of the JSO report says that the 0.5 m optics chosen as a baseline could achieve an optical resolution of 775 m 
from the distance of Ganymede, which is considerably better than is in my chart here.  The difference could be caused 
by (1) a loss of resolution between theoretical optics and what is achieved with an actual CCD implementation 
(2) I don't know what I'm doing in putting together this chart.  Caveat emptor!