I would rather have something that lets me inhale cold, dense air. I ran the numbers and at 45°C(113°F) the oxygen content by volume is so low in comparison to

I would rather have something that lets me inhale cold, dense air. I ran the numbers and at 45°C(113°F) the oxygen content by volume is so low in comparison to room temperature that it actually approaches the level at which the air is considered "oxygen deficient". Of course you'll get the same effect at higher altitudes, but the difference is that you can acclimatize to them in a matter of days, whereas daily temperature changes are to high to enable the same in response to them. I'm no expert, but considering that the body has to work harder to cool off during heat waves the effect could be non-negligible.