Some pretty amazing posts
F25 or 30 as has been stated numerous times are approved flap settings
on the 75 / 67.
There's about 3 knots difference in approach speeds, not an issue on most runways !
F25 gives you considerably better controllability in the 757 with gusty winds, that wing has so much lift already you don't need it all on a blowy day.
It's also quieter and uses less fuel.
Why do you think Boeing installed it ?!