Running the oil down to the minimum allowed should cause no damage.
Measured consumption might be notably lower if the oil is not constantly topped off.
The OM of my old BMW specifically advises not to top off, recommending that oil not be added until the add line on the dipstick is reached.
I would think that the Audi has pretty generous sump capacity in any event.
Most engines intended for extended drains do.
A higher viscosity will not always yield lower consumption.
For example, my old BMW is down to a quart after 2.5K on Maxlife 10W-40, actaully a little less consumption than I saw with the M1 15W-50 I used last summer.
Higher ambient temperatures probably have a pretty linear effect on oil running temperatures, assuming that the engine has no thermostatically controled oil cooler, but the difference between an ambient temperature of, say, fifteen degrees would be very noticeable to you, but would represent only a small percentage change in the operating temperature of the oil.
The change might not be linear, either, since even at 100F ambient, the ambient air is still much cooler than the engine oil or the coolant, so there might be a less than linear loss of cooling, and so a less than linear increase in coolant and oil temperature.
Anyway, I'd go back to M1 0W-40 and see what happens.
It's a recommended oil for your engine in any event, and is much thinner at any starting temperature.