Gator size from 3.7 up to 6.0 required a RDM mast in 2009 and a SDM mast from size 6.5 up to 8.0 m2.
This is still true for 2010 and 2011...
Be carefull about RDM and SDM masts from Severne: they do not have identical bend curves ! Severne RDM mast are rather hard top whereas Severne SDM mast are more constant curve, even for the the same IMCS flex value (430 cm/IMCS 21 or 460 cm/IMCS 25). It is always the best practice to match a sail that is cut for a RDM mast with a RDM mast as intended by the sail designer in order to get the best trim & performance results.