Some of the US East coast flights are so short (e.g. JFK) that it is really a waste for go in F - at least in my opinion. My favourite routes are the true longhauls like SIN/NRT/HKG.
Why not go for a combination of F one-way and return in C (or vice versa of course). This will give you your F experience and save you some miles in your account.
I enjoy the FRA-SIN flights, as they leave in the late evening and you can enjoy the full meal service with caviar and plenty of drinks and then sleep off the alcohol by the time you get to SIN !
