The intention is for the pruning that's already been done to be all that is needed. Should that not prove to be the case (e.g. the 4.5GB database requires too high of a RAM load for reasonable hosting plans), the order of operations for additional pruning would be:
Prune all posts started over a year ago in the NGD - this would remove the long-running (and space-hog) threads and get rid of the bulk of the posts that can/should be pruned back.
Prune posts in the gaming forums (HERO System Discussion, Champions, etc.). This will remove a decent amount, but not as much as the NGD.
Prune any remaining forums (this is the only point at which the rules questions forum would come into play)
Again, the intent is to have the pruning that has already been performed be all that is needed.