I see that some text book answers may be to use a consumable that has a chemistry similar to 4340, like UTP 62 Super Ti, which is stated to be designed for 4340, 4140 etc. But at a tensile of 120 ksi, seems like your asking for problems with high hardness and potential cracking, especially after dilution of more alloy form the parent metal. Seems to me if avoiding a post weld crack, using a low strength filler that is very ductile is the way to go.