If you are talking about Unreal development, Crossfire well not help as the engine did not currently support more than one card. Faster RAM will only help a negligible amount, so not with the cost there either (although yours seems very low speed. Are you sure that is the correct spec. It is usually a multiple of 333). SSDs are great, get one! 
If you are liking to upgrade, then a better GPU would be my first concern. Not that yours is that old.