I can tell you one thing - my D4 doesn’t like towing a 6.5M boat at 110 kph in 45oC

[Barraman]

I had to slow down to 98 kph for it to maintain its normal operating temp on the gauge - probably not bad for pretty extreme conditions. Once the outside temp dropped to 39oC it was quite happy at 110 kph.

[Eevo]

mechanical sympathy

[cripesamighty]

I have a D1 300Tdi and when it's hot (35-50oC), I have to drive it by the EGT and coolant temps, especially when doing long overlanding trips with a rooftop tent and fully loaded. My D3 on the other hand, I haven't hit it's limits yet, but maybe because I don't tow a 6.5m boat! Good effort on watching the gauges.

[Barraman]

I was surprised how sensitive it is - happy to unhappy was often only 2 kph.

[ATH]

You'd be happy in WA as the max for any tow vehicle is 100kph so your vehicle might be happy too. :)
AlanH.