Round trip NY-Paris in business is enough for the PLT challenge. The only benefit to signing up for a simultaneous GLD challenge would be a 25% mileage bonus for one leg of the flight. Not really worth the effort. If it were me (and I've challenged to PLT based on a r/t to Europe), I'd just sign up for PLT.
By the way, getting through CDG on arrival is usually very easy. On the return it can be a real mess - leave plenty of time.