Just some thoughts on this. I have done events in France Spain and Italy and why Wales is not really a bad choice. All these countries have their own foibles.
As a rule I’m happy with cycling in 35c up to 40c.
I find Italy and Spain hotter than the south of France. I know from my winter trips to Asia and south America that it takes two weeks of cycling in a hot climate to acclimatise.
Heat brings its own problems with excessive sweating salt loss and dehydration. If you have acclimatised its no bother but you still need to pay some attention to above.
Above 25c I will drink at least 750mm per 50km even at night when the temperature drops because this is your best time to get your system balanced. Beer works for me if I’m getting some sleep.
If you cannot get savoury food (often the case) bags of salted peanuts hazel nuts etc. Not perfect but better than nothing. Food offered at controls in all 3 countries is usually slices of cold sausage, bread, chewy ham, olive oil (for butter) cheese. Very occasionally clubs have a sit down meal.
Its the very nature of these events to be in thinly populated remote areas. Rural France is depopulating very rapidly in comparison to Ireland.
In France you cannot get a cooked breakfast unless you find a willing foreign owned(Uk/Dutch etc) B&B. Its croissants or similar .
For lunch I have too look up and plan where I expect to be at 12.00 to 13.20 and find restaurants then I need to ring to confirm their open. Then its a 3 course lunch. If you miss this window there’s no where open until 19.00 and they don’t stay open late. Bakers open 6.30 to 12.00 and 16.00 to 19.00 but won’t have a lot of choice later in the day. These are disappearing fast in France in small villages.There are pizza vans occasionally outside towns and even some who travel around villages at night but its happen chance to find one when you want it.
Mc Donalds or equivalent are worth going off route for as they are usually open. French cyclists will not go off route or to McDs. I do my own thing and usually pass them later.
There are some small supermarkets opening in France “Carrefour Express” and again you need to do a search to find them while planning your route.
Carrying a tin of tuna or boiled eggs is a good idea. Taking sandwiches is good for the first day but not good in 35c for day 2.
Excessive sweating. I find it good to have a complete wash using a face towel as it cools and cleans. I change cycling shorts every 200k and wash the others which dry fast on the bike. Water based wet wipes to me are a must have. You are more prone to rashes and fungal infections in hot climates.
Getting drinking water is a big issue and so much so there’s a web site for public taps in southern France. Generally there are taps near the Mairie and 60% of grave yards have taps (many are locked).
Cafes will give you water and I have often asked at houses. Some events will post a list of places with photos of water locations.
Don’t be too hasty to dismiss Wales where you have no language issues and you can get a breakfast roll ………..there’s no big bad wolves either 🙂