I think Joe has it right. Go with what the airlines tell you. And I'd add get there even earlier.
My wife and I flew AA out of Paris CDG yesterday morning (9/30), a 10:30 flight to Boston. We checked in online the day before and all we were told is to arrive two hours before. Having read threads like this here and elsewhere we got a taxi that arrived at CDG at 7:20 (three hours early). At this point you might be expecting my horror story to begin but ... all went smoothly. We went to the self-service luggage tag kiosk and stumbled through that a bit, then to the next line for the security interview. Two minutes tops. Then passport control another two minutes then a quick zip through the security x rays (slowed only by passengers who it seems couldn't possibly have ever heard that, by gosh, they have to put their jewlelry and coins and jackets and devices in a bucket to be scanned so were unprepared). We were in the bright and shiny duty free shop at 2A by 8.
Things did get tricky for other passengers at boarding time. Seems a United flight was cancelled so those passengers were dispersed to other flights such as ours. There was a flood of late boarding passengers and we didn't know why they were so confused about their seating until one next to us explained. I had tracked our flight's on time record over the last several weeks and saw some cancellations, which had worried me. That, with the United situation yesterday, made me wonder: do these airlines have an arrangement whereby they schedule, say, five flights from Paris to the US then, when the day comes, if they realized they have maybe only three planes worth of passengers they decide to scrap one and scramble to reassign the passengers? Maybe that's too cynical. Maybe not.
Which is all to say: whether to arrive two or three or four hours ahead depends on many variables and, yes, go by what the airline tells you. They know the variables. Maybe we got lucky because our flight was early. Maybe our extra precaution of getting there earlier than advised paid off. But my take is that traveling can be stressful enough, and an extra hour of being relaxed at an airport is a good investment.
One final note: I know many experienced travelers cite CDG as inefficient. This was our fifth time traveling through it in two years and it's been smooth every time. Maybe we've been lucky.