I just don't think you're going to get your FL +2 or +5 with F22 at that temp.
F22 has a ductile to brittle well above that temp.
Nickel alloys essentially have no ductile to brittle at all.
However, if you are not comfortable with 625 you might try NiCrMo-10.
In any case, it isn't the weld metal at issue as much as the HAZ's.