Daniel, you really need to discover your personal eyepiece preferences and explore your local atmospheric conditions before you can make an informed decision. It could be that skies in Darwin are more stable than at other latitudes and you might prefer more eye relief than is available with the type 6 naglers (or not!).
A barlow lens is probably the best purchase to start with so you can find out what higher magnifications your skies can usually support. Any chance of getting together with other observers in Darwin to try out different eyepieces?
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