I don't think that AF F is hugely better than AF J. Better, but not a TON better.
If you fly DL or CO you're flying domestic F on the USA segment, and that is ~5-7 hours of the travel time, so keep that in mind. Similarly, the CDG/AMS-IST flight is going to be in intra-Europe J, which is domestic Y+, though that is shorter than the SFO-JFK flight would be.
Finally, depending on which carrier you've banked miles on, you likely won't be able to book into AF F; only FlyingBlue points can do that.
S.