Hmmmm - is it $6,000 better? (the usual $ difference between biz & first on my normal TATL routes).
IMO F is NEVER worth paying full fare for. No matter how much $ you have it's just foolish to burn upwards of 10k for a 6-8 hour TATL flight. However, given the small mileage difference I find it to ALWAYS be worth it to redeem for F over C.