M636 we aren't talking about the vhst in here. We are talking about talgo making a 2 hour journey with the existing line. The VHST is a different conversation all together.
As far as I know, there has never been any proposal from Talgo that suggested that a two hour journey could be made over existing or upgraded track from Sydney to Canberra.
I went to the Talgo presentation at the Australian National University, and all they spoke about was possible percentage time saving compared to existing trains. They spoke of providing a Talgo train set to be hauled by local locomotives, to which it was pointed out that except for XPT power cars, most locomotives were limited to 115 km/h.
The Talgo representatives appeared to have little knowledge of the route in question, and made no claim about overall journey time. They indicated what time savings had been made in the USA and in Europe on existing track.
I have the business cards from both Talgo representatives with their Spanish email addresses if anyone wants to check.
The only way a two hour journey could be achieved would be by constructing some new sections of track.
The obvious choice is to construct the line from Canberra to just south of Goulburn on the alignment suggested for an east coast high speed train. This would be relatively cheap, compared to the benefits, since the route is through open country and near a road I have frequently used.
There could be further savings in time by adopting the former Picton Mittagong alignment (without the later up direction grade easing). New track could be built parallel to the current preserved line.
A two hour journey could be obtained without anything approaching the costs of a high speed line.