To answer your question:
1. I have no experience with booked AF PE but partly operated by DL, DL may give you their economy comfort for you, which there's not much difference/
2. Air France's PE has sky priority, which means you can use the SP line for CI, SP line for security in ATL/CDG, SP line for passport control in CDG, that's a huge advantage if you are in a high season. (although I believe there's no low season in CDG)
3. If yoe're ticketed 057 (AF) or 074(KL) in PE, you are entitled 2*23kg bag, no matter where you depart or where is your final destination.
BTW: I will also avoid A340, unless you would like try on these old birds cause they will be no more in the near future.