Originally Posted by
jackal
I think the OP is in a bit of a hurry to get from CDG to GdeL, and I would guess that RER B to RER A is probably the fastest (by far) way to do so.
That is true, but the conversation I was referring to was about getting around Paris in general. I had seen here and elsewhere how convenient the metro is, many stops covering most of the city, one fare takes you anywhere and so forth. I hadn't thought much about the bus until I heard that suggestion.
In terms of getting to Gare de Lyon, I think the tricky bit will be getting on the RER ASAP: getting through customs, buying tickets, then buying scfn tickets and finding the right platform at GdeL.