@ Bennyling is on the money.
Regardless of which RSP you go with, they all use the same physical network. The difference comes down to the allowance they purchase to cater for the amount of users they have on a particular POI (Point of Interconnect). The allowance is known as CVC (Connectivity Virtual Circuit).
If a RSP only purchases a small amount of CVC on a particular POI, then they sign up hundreds of customers that connect to that POI, performance will drop until they purchase additional CVC’s. As CVC’s are shared between their customer base only.
I use Aussie Broadband and they are quite transparent with this.
You can check the POI you use here: https://www.aussiebroadband.com.au/nbn-poi/
You can check their CVC allocation on different POI’s here: https://www.aussiebroadband.com.au/cvc-graphs/
I paid to upgrade from FTTC to FTTP through the NBN’s TCP (Technology Choice Program). And currently am on an ultrafast package. Speed wise I average about 940mb down and 40mb up.
Sorry for all the acronym’s.