a question for Ethan on Nippon 950gh shafts.

130 is the weight. KBS associate flex with weight so, in the C-Taper:

X - 130g
S+ - 125g
S - 120g
R+ - 115g
R - 110g

You've got to have a fast swing and aggressive transition to warrant C-Taper in x-flex. For example, I believe Rory McIlroy plays PX6.5 in his irons, which frequency at 7.0... and the C-Taper in x-flex is even stiffer at 7.2.

KBS do have a shaft fit system on their website from memory, so may be worth pointing your pal there.

Edit: here you go:

I don't believe the system takes account of hard or soft stepping which is something your pal may wish to consider if he feels he may be in between.