FRS vs Susanoo
As seen here Danzo's Baku enhanced fuuton cut through V3 Susanoo.
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KCM FRS > Base FRS => Danzo's fuuton. Why do I think this? Well for one SM FRS is powerful enough to make an epxlosion bigger than many mountains and very large compared to Nagato's Chibaku Tensei crater:
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You can see how big the CT crater is in this scan:
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That same Chibaku Tensei was broken out of by eight-tailed Kurama.
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Who is weaker than 50% Kurama, which was held down and weakened by FRS.
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Thus we can conclude that FRS is a jutsu much stronger than Danzo's Baku enhanced fuuton. So if Danzo could cut through V3 Susanoo with a slicing attack, FRS would obliterate the whole thing. That puts FRS on par with Kirin, which could also completely destroy V3 Susanoo [
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] but didn't kill the user inside.
If FRS can completely destroy V3 Susanoo, using common sense we can determine that it would do moderate to heavy damage to V4 Susanoo. Nukite is stronger than FRS, which brings me to my last point...
Nukite vs Susanoo
Unlike FRS which disperses energy over the area of a large explosion, Nukite's power is concentrated in an extremely focused attack. Not only that, but it did not have an elemental advantage over Raiton shroud even though FRS did, but Nukite stil managed to succesfully beat the Third Raikage whereas FRS was tanked. Meaning Nukite contains much more raw power than FRS if both used against Susanoo, something without an elemental advantage/disadvantage.
KCM Fuuton: Rasenshuriken already has the capability to do moderate-heavy damage to V4 Susanoo. Nukite would pierce through it completely since:
-It managed to one shot Edo Third Raikage, whereas KCM FRS was tanked- despite FRS having an elemental advantage unlike Nukite.
-Nukite focuses all of its power into one point unlike a big explosion like FRS.
V4 Susanoo does not have the feats to withstand an attack that powerful.