For a US West Coast flight I'd say its worth it - you get 26 hours of F for 2 people for the extra 50k.

Of course, you need to think about next years 2-4-1. I would rather do CW this year and CW with next years 2-4-1 than do F this year and Y next year! Do a rough calculation of how many miles you think you can get from Tesco etc in the next 12 months and then decide.