I'm finding your website extremely helpful!! I do have a question, though.
According to the RER map it looks like it is possible to get the RER C to Versailles at the Periere-Levallois station, but the trip planning websites are giving me much more complicated routes. Is it possible to the get the RER C to Versailles at Periere-Levallois?
I am running into the same issue when trying to plan my trip from Versailles to St Michel-Notre Dame. It appears as if the RER C7 goes directly there, but the trip-planning websites don't give me that option.
And last, will both legs of my journey cost the same amount? (Can I buy a return ticket?)