Definitely noticed this on my sectors over the last month or so. One of my captains last week explained to us in briefing that the reason for our OOL-SYD flight now just topping the 1 hr mark, rising to 64 min (normally about 56-58 min), was because of a go-slow FSO issued to all tech crew.
I asked about the Cost Index used (a time vs cost measure which affects the cruise speed depending on what number is input) and it has been dropped from an already low 30 down to just 10. That puts our cruise speed around Mach 0.76 whereas normal cruise speed for the A320 is about 0.78.
If by doing this it adds only 2-6 minutes to total flight time, which is hardly noticeable, but can in turn save a lot of dollars in fuel costs then why not.
