Looking for smaller cities closer to 40 deg latitude.... any thoughts on Hamilton/Tauranga, Napier or Nelson?
Not many cities on the interior of the island, are there? Seems like almost everything is by the sea.
I know I'm a bit late, but you could always try Taupo? I've lived here most of my life, and it's a beautiful place. Its got Mt Ruapehu 1.5h away in winter for skiing, the lake year round for water sports, great walking/tramping tracks, and it's handy to both Auckland and Wellington.
Just a suggestion

Oh, and wherever you go, don't go to Invercargill. It's even flatter than ChCh, it's full of skinheads, and the weather is usually grey, overcast and drizzly.