It was only impending privatisation which stopped British Rail remotoring
the entire HST fleet with the newer 2750hp (2850hp?) Valenta. Countrylink
probably would have downrated these by 10%.
On the lightly graded BR main lines it would have allowed the standard
consist to be increased from 2+8 to 2+11 and maintain the existing
timetables. For Australia it probably wouldn't have resulted in longer
trains, but the same trains working at higher speeds on any given
gradient.
Cheers
David