Arriving at CDG from Geneva on a Sunday afternoon the middle of June. Would a taxi to St Lazare be faster than RER? I understand the taxi fare to be 50 EUROS for 2 people with hand baggage only...correct?
If you are familiar with the RER B and connections at Gare du Nord for the RER E, the ticket cost is 10.30€ per person and should take about 45 to 50 minutes.
A taxi, from the official taxi queue at CDG, to Gare St Lazare has a fixed fare of 50€ for up to 4 passengers and luggage. Depending upon when you are traveling on Sunday afternoon, it should take about 40 minutes. By early Sunday evening, traffic can become very heavy into the city, lengthening en route times to an hour or more. Taxi drivers are not tipped.
I always take the RoissyBus. It leaves every 15 minutes from right outside of arrivals at CDG, and brings you to the West side of Opéra Garnier on rue Scribe (7–8 minute walk to Gare-Sainte-Lazare). It costs 12€ per person, and has no changes, stairs or escalators. Plus you get to actually see the city on arrival rather just bthan tunneling underground. And on a Sunday mid-day, the traffic shouldn't be too bad.
https://www.parisaeroport.fr/en/passengers/access/paris-charles-de-gaulle/public-transport/roissybus
If you choose a taxi instead, they will take luggage above and beyond just hand carried.