My vote would be a good 10w40 or 15w40, it probably doesn't even get cold enough there to require a 5w and a 10/15w will have better HTHS and viscosity retention. Do they sell Valvoline durablend over there? That'd be my go-to, pretty much the same as their 10w40 Maxlife (probably without seal conditioner) which is tough as nails.
Yes we can use 15W40 year around, and Castrol GTX 15W40 UltraClean semi-synthetic (SN/CF, A3/B3) is often on sale at very good prices.
Yes we still get DuraBlend, but a bit hard to find, as it's more wholesale to garages now. Their regular retail semi-synthetic is called EngineArmour, but it's mostly the same, when I asked Valvoline on the phone once.
Right now it's on sale at AutoBarn in Oz until 24 Dec.
Valvoline EngineArmour semi-synthetics in the 6L jug,
All 30% Off at $35 for 6L,
15W40 API SN/CF, ACEA A3/B4.
10W40 API SN/CF, ACEA A3/B4,
10W30 API SP, ILSAC GF-6A,
5W30 API SP, GF-6A.
Two of those bigger 6L (6.3 quarts) jugs, would do the OP for 3 oil changes. I've used a lot of Valvoline 10W40 semi-synthetic over the years, a fine drop.