The best climbers in the world are racing in that France at the moment, why not have a look at the bikes they are riding for a few tips?
except for one minor detail i would agree, thing is, is the OP a pro with a decent level of fitness, flexibility, and no beer gut?
Something with a compact crankset and an ability to spin not honk. Oh the 52/39ers will scoff on the first hill or two, but a hundred miles in 39×25 is not so funny.
did 135miles the other week including the Forest of Dean, Malverns and Gospel pass with a 53/39, 13-23. I survived. and i am only average fitness
Gearing isn’t that important in the grand scheme of things, the difference between a compact and standard chainset isn’t that great. The only place it matters is if your doing steep long climbs or horrifically steep short climbs, the climbs that are few and far between in the UK.
Most climbing is in the riders head, accept it hurts occasionally and you’ll ride most things.