Only you can tell if it's worth it for you. Personally, I wouldn't hesitate one second - the difference between CX J and F is definitively worth 50k of my miles! This comes down to seat comfort and service - I'd even say the difference in seat comfort alone would do it, even though I do value CX J.

Taxes will be the same so that shouldn't make any difference. +1 from me to go for F - you will love the experience, but only you can tell if it's worth 50k for you.