You may want to keep in mind should you commit to a contract, is that Retail Service Providers (RSP’s) offer various speed tiers, and may upsell “higher speeds” where they can.
My recommendation is this: if you do commit to a contract, sign up for 25 Mbps, until such time you know what your phone line is capable of delivering. Then make an informed decision based off what the modem says it is capable of delivering on your line.
No RSP nor NBN can tell you what speed your line is capable of until such time your modem is connected and NBN activated on your line. This is part of the uncertain nature of the copper network.
The capability of your line will more than likely change as weather conditions, corrosion, maintenance work, and a myriad of joins fail.
Over time, your speeds will not improve they will get worse as the copper corrodes and joins fail.
Gleneagles Estate NBN Committee