Hi,
not really I go as far as I go. under 30°C in general freeze lightly. On moderate temp. 30-40°C I go normally my longest distances. So for me heat begins at 40°C.
Over 40°C I may longer rest in supply stations (gas station, Shops, Shade). Normally 2-3L per 100 km (during the day) is enough for me. If the temp. rise to 50°C I can't drink anything cause it tastes bad (I should try hot drinks like coffee, tea). I didn't cut down. In Namibia I got heat sick and started vomitting while cycling. I didn't want to turn so I proceed to the next house (120 km). If you have more than 37°C you really have take care. Your body overheats and you're permantly in fever. Then it's necessary to cool down (e.g go swimming)
My general strategy: Drink in the morning, make your hat wet (8-10 times per day), make your cloths wet (in Sri Lanka we lay under fountains), sleep in air conditioned rooms, don't drink (ice) cold drinks during the day, reduce the pace. I prefer the wind while cycling instead of resting. Rest are normally longer than normal (I friend said: Your third cigarette helped my to survive - the planned 15 min break was extend to 45-60 min.)
Thomas