Below 85 is not going to give you huge problems. You could consider running a CO2 system which would allow you to boost your temps up even further.
I used to live in a house with a curtain/French drain too and it had been installed because the cellar DID tend to run on the wet side. Surface area determines rate of evaporation if all other things are equal... the large open wet floor evaps more than the water in the drains. Hm. I have to think about this. You know, a nice tiled cellar floor adds value to your home...