There is also a service called "City Locker":

http://www.city-locker.com/mobile/mo...tour=mobile_01

Who have luggage lockers in a few locations across the city, including Gare du Nord (although I've never had the nightmare waits there mentioned above - in dozens of visits). The most convenient is perhaps the St Michel one, 5 minutes' walk from the St Michel Notre Dame RER station, which serves both Anthony (for Orly via OrlyVAL) and CDG, and is right in one of the tourist centres of the city. You can pre-book and pre-pay space.

Personally, I wouldn't have any qualms leaving my luggage in such a place, but I mostly own very little of value... And a day in Paris? Where's the downside?

2E-2F in 1h40 is definitely doable, but only if it's through-ticketed. On separate itineraries, I'd steer well clear.