Even diesel locomotives from the 1980s aren’t particularly clean.

https://www.epa.nsw.gov.au/your-environment/air/non-road-diesel-marine-emissions/reducing-diesel-emissions-locomotives

https://www.epa.nsw.gov.au/-/media/epa/corporate-site/resources/air/diesel-locomotive-emissions-upgrade-kit.pdf

I’d assume V/Line would one way replace the locomotive hauled trains on the Swan Hill line with VLocities, but they’d need to complete the level crossing and stabling upgrades on the line, similar to what has been done to the Bairnsdale, Shepparton and now Warrnambool lines.

As for V/Line trains being slower than when the VLocity trains were first introduced, the “headline” times were for a single express train to Melbourne in the morning, and a single express track back in the evening – in the years since they’ve added more stops to those runs.

https://the-iron-road.blogspot.com/2019/02/ballarat-to-melbourne-in-under-hour.html

Southern Shorthaul Railroad’s broad gauge in Victoria are mostly B and S class locomotives built between 1952 and 1961, so they’ve still managed to half the age of their fleet.

Back in the mid-2000s the locomotive hauled stock was supposed to be replaced by VLocities, but growing patronage kept seeing that idea kicked down the line.

Sadly V/Line have not modified the broad gauge V/Locity sets for long distance operation, and a trip out to Bairsdale warrants hearing protection.

A side note, I find about travel times for the V/Locity sets in 2005. https://www.theage.com.au/national/fast-trains-strike-costly-sound-hitch-20051011-ge111s.html
“Only the Geelong trip, at 45 minutes, will be as fast as originally spruiked.

Other times: Ballarat 64 minutes, Bendigo 84, Traralgon 95.”

However, the current timetable has Traralgon taking 141 minutes from Flinders Street or 147 minutes from Southern Cross, for the outbound morning express service. About 50 minutes slower than the revised estimate.