Just a heads up - it's believed that there is a difference in the wheel profile of the XPT versus the Overland NR/93 class + carriages that would be the main users of the SG track into Southern Cross. This may be, as alluded to earlier, the issue that was not properly accounted for (or was accounted for but the solution didn't address the issue adequately).
Yes, there is a difference. It's my understanding that the difference wasn't even discovered until the investigation following the derailment.
I would think that the main user of the SG track over the flyover will be VLine, with three return trips to Albury a day. There are two return XPTs daily, while the Overland only runs three (?) days a week in either direction.