The RG65 Class has an unlimited variety of weights and lengths of fins and bulbs - the DF doesn't - only two are "authorized" .
The RG65 has a maximum limit on the height of it's mast. The DF doesn't - only two smaller masts are "authorized" .
The maximum sail area allowed in the RG65 Class allows for more sail area (and less if desired) than that of the DF Class. You get high wind sail area choices in the DF - but not light wind sail areas.
The RG65 allows for ANY choice of servos/winches. The DF Class does not.
The RG65 Class allows paneled sails - OR - single flat panels. The DF Class allows only single panel sails.
The RG65 Class allows swing rigs. Not so in the DF Class.