danepak: Spark will switch my mum in law over to unlimited ADSL early January (not sure if I mentioned it earlier, but she's on 10GB at the moment, which is adequate for her - however we'll use that in a few days), when we arrive. No contract, so we can cancel, if we can't agree to a deal on the fibre.
Chorus won't do any installs before late January anyway (at the earliest).

So I got Spark to switch us over to unlimited ADSL. We currently pay $99 per month (unlimited ADSL and phone line) through Spark. The other week they had a special, where we could upgrade for free to fibre 100/30.

Placed an order and Chorus has already been once. Two more visits required, but until now, seems like a smooth process.