Not sure whether the OP does, but an AT thread pattern will have a negative impact on fuel consumption as well. Not sure whether Australia has the ratings but it may be worth comparing EU or UK online tyre sites and check the rating of the tyres. There are some huge differences.

I find the Pirelli Scorpion Zero with noise control really good. On longer journeys gets me consistently about 20mpg, and around town I go down to about 18mpg with the 5.0V8SC that is...

AT thread pattern will have a negative impact on fuel consumption as well

you are right, i have no idea
i will google it RR 2005 4.4 petrol
Any spelling mistakes are the fault of spellchecker
Previous MG J2, CITROEN light 15 x 2 gone unfortunately
Present MERC 180e, RANGE ROVER L322, JAGUAR XJS, MERC 280SE, MG F, JAGUAR S-Type 6v 2003, jaguar s-type 8v 2004, Ford Cougar

Cant find anything about AT tread pattern
It seems I have symmetrical type tyres
quote
Symmetrical tread patterns: comfortable and cost-efficient
Unlike directional, symmetric tyres can be fitted and rotated in either direction as both halves of the tread pattern are identical. They are particularly quiet and provide good roadholding. Their lower rolling resistance reduces fuel consumption and extends the lifetime of the tyres. They are often used for commercial vehicles and provide – like our RainMax 2 - good value-for-money for those that mainly drive short distances. RR 2005 4.4 petrol
Any spelling mistakes are the fault of spellchecker
Previous MG J2, CITROEN light 15 x 2 gone unfortunately
Present MERC 180e, RANGE ROVER L322, JAGUAR XJS, MERC 280SE, MG F, JAGUAR S-Type 6v 2003, jaguar s-type 8v 2004, Ford Cougar

Which tyres do you have on your car? Full make, model, size

At the moment 275/45r20, different makes.
Had a look today to see if the 275/60r20 would fit.
They wont.
After measuring the room for the tire, I don’t believe 55s would fit either.
The maximum dia I found on my vehicle was 31.750”, give 0.125” clearance and I am left with 31.5” dia
The original tyre 255/ 55r20 is 31.4”, so I guess that is the largest diameter tyre I can fit.
Any one want to buy some nice second hand tyres 275/60r20 RR 2005 4.4 petrol
Any spelling mistakes are the fault of spellchecker
Previous MG J2, CITROEN light 15 x 2 gone unfortunately
Present MERC 180e, RANGE ROVER L322, JAGUAR XJS, MERC 280SE, MG F, JAGUAR S-Type 6v 2003, jaguar s-type 8v 2004, Ford Cougar