Wow that was quick and really detailed, thank You very much !
This is in deed enlightening and astonishing.
The summary is that You can't even save much weight unless You have an older bike.
My F4S has, according to the Manual, steel flanged 310mm discs.
Swopping them to F4 1000S 310 mm alloy flanged discs is saving around 750 gr or 1,5 lbs.
This is in my eyes probably the way to go than.
Everything else seams to be weight wise pretty much in the same league.