One-time, irreversible decision. Take the guaranteed monthly check or invest the lump sum yourself?
This is an irreversible election. Real-world considerations not modeled: PBGC insurance limits, your employer's pension funded ratio, COLA on the pension (or absence thereof), survivor benefit elections, your discipline to actually invest the lump sum, and your tax bracket if rolled to an IRA. If your pension's implied return exceeds 6%, the pension is hard to beat with a balanced portfolio.