I've done the vast majority of my DSO imaging with both unmodded and modded DSLRs. My cooling mod was only a recent addition to survive the QLD summer...
Down in your neck of the woods I'd expect 5 minute subs with your camera at a suitable ISO to be very effective. The Sony sensors in Nikons usually fare better than those in Canons.
I'd suggest favouring f-stop over stars though...you can always crop
