Well, until July last year, I was living in Wahroonga with my baby, and paying ~$1700 after the 50% NCB (23 y.o). As far as I know, Wahroonga is one of the lowest risk suburbs around Sydney, so this might affect the price a little.
However, I think the price on yours is a bit steep for a "medium risk" suburb, considering you're now 25 and the premium on 6's is less than 8's. What model is yours? EF/EL/AU?
In general NRMA have been pretty cheap for me, but obviously not for everyone. I'd be asking for a breakdown of the policy price if I was you.. or shop around. Seems steep.
Let us know how it goes mate.