I have one question: Do you really want to sit out the next 6 years, watching opportunity after opportunity to start working as a pilot go past you?
If you think you have the patience for it, go for it. If not, you know the answer already. Personally I would sign up for the extension, you never know. But one day you could be faced with
the dilemma, a letter of offer from airline X on the one hand and your lump sum and pension on the other.
What to do, what to do?