One last note to add to Al's Gospel about using manufacturers design selections.
Fabrication and Repair are two entirely different worlds.
Filler selections for fabrication may not be the same fillers chosen to do refurbishment.
All the first tier manufacturers of aerospace gear have standard practice welding manuals to help their engineers make filler decisions or engineering variences. Remember service conditons, heat, friction, vibration, any cyclical type load may have a bearing on filler selections.
My guess is that the selections you are trying to make have already been made... Your task may be to find out what the manufacturer wants you to do.
Just for personal study I like:
ASM Metals Handbook Vol. 6
Superalloys a Technical Guide
http://www.asminternational.org/Template.cfm?Section=Bookstore&template=Ecommerce/FileDisplay.cfm&file=ACFAACF.pdf