Vlocity's like nearly all later rail vehicles the maximum speed is set in the control system. The engine and gearbox for these are capable of 200kph. In all the ones I have timed the maximum speed is between 160 to 167kph.
The Vlocity's take around 7 to 8 kilometres to reach 160kph, a grade in excess of 1 in 100 will prevent it from reaching 160kph. This means there only capable of 160kph cruise if stops are MORE than 50 kilometers apart. On the Bendigo and Ballarat lines for instance services running to the country, 160kph running is only availble for small part of the distance.
Even on the NE line simulations show the only place 160kph saves a signifiant amount of time is between Avenal and Euroa.
As others have already stated 130kph runnings is easily availble, A Vlocity can reach in 130kph a very short distance, so can show quite significant timing improvements even on N class hauled 115kph services. Such speeds can made availble on the current rail system with a relatively cheap cost.
On the current Geelong line, its unlikely 200kph running using Vlocity's would save more than a few seconds over a good 160kph run.