Although it's my understanding that IFHE allows russian light cruiser guns to do a good deal of damage too.
IFHE + Demo =
For 150-180 mm guns anyway. I don't have enough skill points for my Atlanta captain yet, but it is frightening to run into one. All of the Russian cruisers T5-9 benefit from IFHE. Cleveland would too, but I take Concealment Expert first for any cruiser. And the Belfast was good (bad?) enough already without IFHE. Finally, the Mikail Kutuzov really needed a buff... NOT! Sure is fun though.
203 and up HE shells can already penetrate whatever they are going to without IFHE.