In case anyone is interested, I contacted Mike at Toowoombah BMW like some have recommended and this is what he has come up with:
Allianz issued product:
BMW product (underwritten by Allianz):
$3818 2yrs (RRP $6491)
$4500 3yrs (RRP $7700)
He said that there wasn't a great deal of difference in the two and he mostly sells the Allianz issued product. The BMW product is the only one that offers a 3 year option though.
I've just got to weight it up now, $4500 is still a bit of money for effectively 2 years cover (due to the fact i've got the premium selection on the car, which'll be overwritten).
Hope this helps someone.