I would say that the strength requirement for Katanas is on the low side. They're rather huge swords, and to wield them with one hand (as BGII characters do) one woud need far more strength than is required for, say, a long sword.
Actually, I would say that 9 STR for katanas is "just right"...
You see, although katana _is_ a rather huge and weighty sword, it has a very unique design -> when you hold it properly (by it's handle :-) ), it feels _extremly_ light (because of it's design which shifts the weight balance towards the handle) - almost like you're holding a "paper sword"... This is why katana is such a fast sword.
I suggest *increasing* the DEX requirement for katana to at least 16 (or even 17). Hey, it's a very, very fast sword. One needs a good hand-eye coordination in order to *not* decapitate one's self... ;-)