SPS may differ from the traditional PS pension as it was launched in a different economic era.
Here is a crude calculation based on a traditional pension (not coordinated). I am omitting the lump sum and future indexing for convenience.
John is retiring at 55 with 30 years service on a pensionable salary of €80,000. His preserved pension is €30,000.
Lets first say he pops at 68. If he opts to take this Preserved Pension at 60 his annual payments will have amounted to €240,000. If he had instead opted for CNER at 55 his annual pension of €23,400 would have amounted to €304,200. So an advantage of €64,000 for CNER.
Now say he lives until 88. His Preserved Pension payments would then cumulate to €840,000. If he had taken CNER his annual payments would accumulate to €772,000. Now it is advantage €68,000 to the Preserved Pension. A reverse in financial fortunes!
In this example the crossover age for advantage to the Preserved Pension over CNER would be approximately 78 (below current average life expectancy).
The Preserved lump sum is also more favourable than CNER - apart not being actuarially reduced, it is calculated in relation to the salary pertaining to his grade at 60 instead of 55 (when he actually retired/resigned). And salary-linked pension increases after retirement are also likely to favour the Preserved Pension option.
In general for traditional PS pensions the financial balance between CNER and Preserved Pension will shift gradually and linearly with increasing survival age. Fortunately for the government the actuarial tables have not been re-adjusted to reflect this increase in life expectancy.