Don't know about JFK-SFO, but on JFK-LAX the 762 in F is quite a bit better than J (even factoring in the 763 J seats instead of the 762 J seats). Individual DVD, better food including lobster, etc. Of course the 762 seats recline 180 instead of the 150 for the 763. Having 2 FAs for 9 pax also helps.