These are some patterns which I observed. Not sure if they are accurate.

Actually pace of promotions will be rather fast in your first 5-10 years in civil service. But pace of promotions will start to slow down in your 30s. A lot depends on CEP.

AD CEP (MX11A)
Default CEP for most people. Worst case plateau at MX11A (plateau at 8.5K) by mid 40s. Not difficult to upgrade to SAD/DD CEP.

SAD/DD CEP (MX10)
Majority will reach MX11A by late 30s and hit MX10 (plateau at 11K) by mid/late 40s. This is easier said than done. You need to not screw up for 20 years to achieve this. Any screw-up goes back to AD CEP.

Director CEP (MX9-level 1)
A few exceptions will reach MX10 by mid-30s (plateau at 11K) then hit MX9 (plateau at 12K) by early or mid-40s

Senior Director CEP (MX9-level 2)
Very very few people make it this far. You must have a string of AO bosses (non-AO bosses harder, usually they will be demolished by AO bosses during ranking unless super senior) who loves you to get here. The problem is AO bosses are very very demanding as well. So far only seen one chap made it. Same as director CEP. but you will cross the MX9 bar in your late 40s and plateau at 16K instead

From my observation, I think there are two or three levels of CEP for MX9.

Let me know if my observations wrong. Help me by affirming/refuting my observations.