I see where you are going with this TPC...

Although I am not yet jumping on the "big sword = AP" wagon, and I said "light troops" as an example (not claiming that running down skemishers was the role of catas).......

......I can see that, in the case of the Parthian FM, it does make sence if you are trying to simulate the other AP weapons they carried. Since the RTW engine won't let us. Other than that I am not convinced that long swords were armored piercing/breaking/trauma causing weapons by swinging them (unless you get a good swing at a guys head). You may have better chances at getting through mail with a powerful straight stab, but with plate (iron or bronze) forget it. And catas use small metal plates.

Another thing..... Be mindful that as a result of reducing attack and lethality to give a good working AP to Parthian FM (and not overpower them) they will be less effective against units such as the Theuroporoi (sp), Bataroas, Hoplitai, etc due to the lower lethality of the weapon, and the lack of heavy armor these guys fight with. (again RTW engine issues, maybe in EBII something can done about this)