I know it's not CCP4 but I use moleman2 for this, http://xray.bmc.uu.se/usf/xutil.html
. You read your pdb into moleman and choose the STatistics option, it
outputs Rg among lots of other things. It can all be scripted too if
you wanted to say charge through the whole PDB and get Rg for
ever
I have found that ion exchange is a good way to concentrate protein.
If there is no reason that you can't pass the whole 450 mls through
the column then you should do that. Another way to do this would be to
add ion exchange resin straight into the 450 mls, stir for a bit, let
it settle, po
