At risk of sounding like rock man, this is excessively blue sky...

At risk of sounding like rock man, this is excessively blue sky thinking. For the record I am still incredibly bullish on E25 HPMSM business but don't think every aspect of their business needs to be viewed with the rose tinted glasses.

E25 cannot even run a super quad (60m quad config with net weight ~150t), they're currently using 115t net weight standard quad.
This is under MRWA performance based standard if you want to do some reading / view allowable routes
HVS Network Map - Mainroads WA

I also believe MRL may be overselling the 'automation' side of things. My understanding was they are only allowed to travel in a convoy of 3 trucks, manned at the front and manned at the back with the middle truck fully automated. Maybe the drivers of the escort aren't 'driving' as such but there's only a 1/3 reduction in labour requirement. 320t on a public road seems unlikely, so they are either committing to a maintenance schedule that likely offsets the benefit or they are doing it on a predominantly private road (again maintenance or construction of that road wouldn't be cheap which isn't considered in their 50% haulage saving) with the last mile of that potentially on public road (would have to be agreed by MRWA)

Source:
"We will also build, own and operate all project infrastructure including a private, 150-kilometre haul road, port infrastructure, transhipper wharfs and two Onslow Resorts which will accommodate the project’s workforce," the statement added. Mineral Resources confirms FID for Onslow Iron project in WA | Mining Digital

Ashburton would also be able to electrify their fleet on a 150km haul more simply, for E25 to do it on a 500km haul would be a huge challenge given the battery range for heavy haulage (they could get about half way and add in a battery swap to achieve this but that adds time and cost).

Not saying any of this is impossible, but the logistics for Ashburton project v Butcherbird are much different prospects and it's important to understand the challenges.

On the flip side, I believe E25 have an incredible advantage in their resource - low impurity ore that can be made into HPMSM without requiring electrolysis. This is the gamechanger.