And I was thinking finally some intelligent discussion ….

A6 , in practical terms the ruleing grades Sydney Melbourne are 1:40 on the down (all south of Goulburn) and 1:50something on the up (the climb from Wagga Viaduct to Bomen) .

I don't believe the grades are an issue for pass or interstate freighters .
The power to weight ratio of dedicated pass trains makes it a non issue and I'm sure if you went to the freight operators and said we could can the curve/speed issue but not the gradients they would sit up and listen .
The AC diesel electrics laugh at the grades and make the DC ones look sick by comparison . Getting OT but when a 93 (x1) can drag 1700T up Como in the dry at 25 km/h and never even look like slipping they prove their worth . Also had two of them drag a 4600T steel train , with a dead NR on the front , up Jerrawa at 16 km/h .

Now for high speed perway , I have not researched it but I'm guessing reliable 200+ km/h perway is probably going to look a bit like the US standard stuff eg 30+ TAL rated rail/sleepers/sub base .
And this plays right into the hands of decent freight train equipment and performance .
To give you an idea of what North American AC traction diesels can do I've been there in WA with SD70s (x 2) pulling the best part of 6000T up 1:67 1:68 grades at 25 km/h . And these trains were not quite 3000 metres long .
I am not suggesting we could run these units over here but with full fuel loads and a bit of ballasting American style I think we could get the GT46ACes and AC44s up to around 150T . Three of these would make short work off pulling trains of similar weight up 1:40 grades .
Now before people start howling about hurting Mr Diesel by working him hard , or crawling up the ruleing grades at 25km/h , have a think about how fast the trucks aren't going up their ruleing grades . This is what the superfreighters are competing with .
The steepest grades won't be a big part of the total distance and you can run pretty fast down steep grades if the alignment is suitable . It's the average speed not the up hill slog speed that is important .

Where our rail ancestors let us down was building lines where minimum gradient took priority over curve speed . 90 years later we need to get over this and build lines that are straighter and faster even if it means some steep but acceptable gradients .
The pay off is shorter transit times between the Capitals .
And one more thing , I believe that if we continue to persist with the current dark ages type rail alignments that everything on them will eventually fall prey to alternate modes and die out completely.

As for the aspect of modern diesels and their abilities I completely agree with you again, when the 81's arrived they were given the tag of Depot Destroyers/killers owing to their abilities, over what we worked on prior to them.

The aspect that I have brought in is no more than the concept of gradient easing and realignments, I am pretty sure that if the Short South new line is done properly it would be no steeper than 1:100 as the ruling grade, that aspect is to satisfy the first stage of the overall main south and meet the purposes of the Canberra services.

South from GLB is the issue of not just the grades but the actual overall alignment of it, which I believe plays a bigger part of the problem facing rail into the future. The ILR has a huge advantage as much of it will be new line and the old lines built up but I still wonder to what amount either especially over some the terrain that its proposed to be constructed on, and how strong they build it especially with the sub soils in certain areas.

The overall Main south incorporating the Short South needs to be a term project and complete sections at a time with a concentrated work force.   I have an old fold out diagram of the line from Sydney - Albury, and when its laid flat and in the 4 sections the line looks like the trail of a drunken snail or ant, so much is the wriggling of the line.  A reason also why debate has come up in the past about going back to the old alignment, which had steep grades but straighter alignments, a fair idea up to a point but all that would do is replace one old incapable line with another one around perhaps 5% better and at what cost benefit?

I would also add that the need to do the Southern line up has an equal competitor for that money and that is the NCL with its multiple needs.

Rather than looking at a VFT, HST or the like terms and wants, I would prefer to look at and promote the concept of a RFT that being Reliable Faster Trains.

Looking back on when the XPT came out to which I was qualified for, I know of no area where the track speeds were not reduced for normal passenger services and the TT's also extended so the XPT could maintain the speeds that were required of it. In general all boards below 100KM/h were reduced anywhere from 5 -15 KM/h for loco hauled trains and after a while even the X's had their speeds cut in many areas especially those areas that had 110 -115Km/h speeds.

Certainly the A/C loco's and even what I find with the modern ETR sets is their abilities in acceleration, something the X dragged at but won out owing to overall speed.

There are quite a few hills on the hume that tax the truckies, but yes, as the newer trucks keep coming out, they have great power and can get moving quick, especially when they are on the super highways that give them every chance to win the freight battle against rail. In that sense the interstate rail freight industry is on the losing side ATM even when the ILR comes into being owing to the competition from road.  Rail cannot go to the factories and pick up the loads in rail vehicles, and by the time any potential freight is ready, a truck can be already 1/4 of the way to its destination.

Where we live now I travel on the Hunter line quite a bit and have noticed how much larger the ballast is that's being used these days, it has slowly increased over the past few years to a size that is quite large, a couple of sections of note is around Metford. But, its possibly the result of the heavy coalies but I do see a benefit for other freight services though.  Not sure if the big rocks are used past Maitland though.