If the PDB (#1) is already fit to the map (#0) you could create a
simulated map for the pdb then measure its correlation with the
experimental map:
molmap #1 12.5
measure correlation #2 #1
The 12.5 in the molmap command is the resolution for the simulated
map which should match the experimental map. By default the
correlation will be measured within the displayed contour level of
the first map given in the command.
The commands are described in the Chimera User's Guide.