The trick that everyone seems to use to legitimately avoid infringing on any copyrighted material is to use "equivalents". If you want to talk about how a certain unit performs against Tn Ax opponents, find a common model with the same stats, and talk about how your unit performs against it. The common ones, as you probably well know, are Marine EQuivalents and Terminator EQuivalents, but there's no reason you can't add more to the list. If I say that my Dire Avenger will cause 1/162 wounds / point against Wraithguard-equivalents then there's no copyrighted material given, and no way to work out any copyrighted material without already having most of it already - you'd have to know the stats of one unit, and the appropriate tables, to work out the stats of the other unit.
You're probably even safe talking about wounds / point vs. T4, for example. But then you get yourself in trouble the minute you want to talk about an example. I believe you can say "Dire Avengers wound T4 50% of the time" without getting in trouble, but the minute you want to add "Daemon Princes, for example" you're in trouble because you have (incorrectly, obviously) identified Daemon Princes as having T4. Whereas "basic-human-equivalent toughness, like Dire Avengers" should be safe, so its probably a better way to go all round.
(It should be noted that I may or may not know what I'm talking about. These are my best interpretations only, of the rules posted
here. I've rather deliberately pushed the edge a bit above in the most harmless way I could work out, in hopes that the mods will sort me out without whacking me with the banhammer if I'm wrong. If you're reading this still, I guess I wasn't too far off?)
