In particular, if it runs through loading coils, or a mux at any point, it isn't going to work. Telstra is free to install a mux at any time that'll break things badly. In practice, they haven't so far. Normally, you want to install the PAPL, and borrow some modems to make sure it'll work. If it doesn't, you've only blown the PAPL install costs.
Thicker copper is better than thinner.
The gold plated option. This is where Telstra supply an X.21 interface at each end point, and take care of moving the data between them. K Telstra control the speed, but you can normally upgrade it or downgrade it fairly easily. Normally Telstra will quote you about a month to install it, and actually take around 50 working days. You can think of this as an almost exact parallel to the PAPL solution with a radio link instead of the wire in the middle.