I'm planning that route next May-June. Starting St Malo, down to St Nazaire then along EV6. I'm going to divert to watch a few stages of Criterium Du Dauphine beg June, including Alpe D'Huez 10 June, then up to Basel and along EV15 to Dusseldorf in time for the TDF. Back home across Belgium. I rode down to the Pyrenees mainly along EV1 during May/June this year, I'd say it was a good time weather wise. Hot some days, but never too cold and very little wind or rain. Might bump into you if you're travelling at the same time!