from CDG to Gare de Lyon

This may be tight. Since the Les Cars/AirFrance shuttle says they can make it in one hour, a taxi should be able to do the same. Using RER, you can get there in 59 minutes, but you must get the 9:41 train to get there by 10:40. The next train gets you there at 10:55.
Where are you going?

A taxi is much faster than a bus. On a really good day, I could drive it in about a half hour if I made most of the lights. Forty-five would be comfortable on a week-end. I know in my conceited heart that the taxi dude probably knows more than I do. You've still got some more slop since you don't need the full half-hour from the front door of the station to the platforms. You say you'll know your way around the station. You know there's two sets of platforms, right - - one batch well east of the front doors? I wouldn't take the bet during the week.

I will be going to Nice with my friend who will be at the station waiting for me. It will be easier for me to take the taxi because I wont have to waste time figuring out where to buy tickets etc for RER.

When you say 09:30, are you allowing for the time you will need to stand in line at a taxi rank? What time is your flight scheduled to arrive?

The summer schedule shows TGV direct trains to Nice from Gare de Lyon at 10:49 & 11:41. The 9:58 from CDG connects with the 10:49 train from GDL at Aix-en-Provence.

My flight will arrive at 8:20 from Munich so I will only have to collect my checked baggage and go through custom.