I would question the comment that SOP's are rigid and gospel. I've flown for too many operators whose SOP's changed with every change of Chief Pilot. They each had their own favourite way of doing things. Some were good ideas, some were crass. Common sense/airmanship should always prevail. That's what we are paid for.
There was one C.P of a London based Loco, who demanded Gear down at G/S alive. What a classic way to waste fuel. Had he never heard of Low Drag. low noise, low fuel approaches? Then the London Airports demanded these type of approaches, which most of us had been flying anyway at every airport for decades. Guess what, the SOP's changed to suit ATC.
As for C.I's. I thought that zero was min fuel. Also, I did fly for 1 operator who tried the Boeing ideal that C.I. should be selected for each sector dependant on fuel % price; i.e. a variable. What a fisco that was. LRC seemed to work fine for most trips.
I heard it said that ej's first B737 C.I was chosen to match Stelio's age. If correct, how scientific was that.