At risk of being glib - SOTA is the perfect activity when it’s in the 30’s (but low humidity). With the rule of thumb of -10 degrees per 1000m, climbing a hill is the solution, not the problem! We have a 1700m range behind our house and there have been a number of hot muggy summer nights when the southerly fails to kick in that I’ve headed to the tops for the sole purpose of a good night’s sleep!
On a less glib note, the answer to operating in heat is hydration, acclimatisation and shade. Our summers here in Central Otago’s ‘desert’ country generally sit in the low to mid 30’s - with occasional forays into the low 40s - but not for a few years now. The hardest day, however, is not the mid summer heat, but that first spring day when it gets above 25 following a crisp cold winter. The body goes, ‘I can’t do this’ and yet you know there’s at least another 10 degrees to go till full summer. But by the time the 30’s arrive, you’ve generally got used to it.
I carry a minimum of 3l water and expect to fill it as much as 3 to 5 times a day working in full heat; 6l if working with the dog and limited available water sources. I always wear a wide brimmed sunhat. Good UV-blocking, wicking clothing (we have brands Swazi, Stony Creek, Huntech here that specialise). And an easy, steady gait. I find that when I get up beyond 3 or 4litres a day that I need to include salts in my hydration - poweraid or gatoraid powder, or the less appealing rehydration satchets that come in 1st aid kits and they hand out on firegrounds.
For work, we manage 20km+ days of weed / pest animal surveillance or trapping in those conditions comfortably. What’s harder are the days in full PPE dragging 100’s of meters of spray hose, or lugging chainsaw or scrub-bar. Or - hardest of all, in full firefighting gear - that really shows you how much liquid you are capable of consuming!
Like you though, I look in awe at VK and the like, where they manage all that at either 35+ degrees, 100% humidity or 45+ and dry air. I think that must really push the limit.
I recall the day I finally emigrated ‘permanently’ to VK after a few years on work visas. I spent the night sleeping in the car in Langsett (S. Yorkshire) at -8, (having spent the night at the pub catching up with old school mates and got locked out of the YHA), then arriving in Melbourne to a record 47 degrees and an invite to a BBQ at a mate’s place in Frankton. That was a shock to the system!