Litespeed: I'm in Wellington and I cycle commute from Tawa into the CBD most days.
I've just started cycle commuting again - same suburbs as you :-)
For years I used to ride a racing bike for this but something's a little stuffed and I haven't got time to figure out what it is and fix it. So, I'm relegated to a mountain bike. I'm finding on average it's taking me ~40 mins to the CBD and ~45 mins back home - via Ngauranga both ways.
Being an ex-racer I'm really enjoying the exercise and am saving a heap in vehicle costs at the same time. I'm one of the fortunates who has never been knocked down by a motor vehicle although I've had a number of close calls when cars have cut across my path at intersections, including a car which turned into me and struck my back wheel because the driver "didn't see" me.