Does Heroic edition have any changed monster rules?

If not, I'd be inclined to make Precision Strike a little less powerful, simply to draw out the combats a little [i can't think of many things below CR 6 that'll survive one hit from the Fighter as written]. 3-4 round combats with movement and choices are interesting, 1 round combats usually feel like a game of Top Trumps...[if you have no idea what that is, sorry...]

It's not clear how the Weapon Focus and Weapon Specialisation abilities function together. Do they stack, trigger under different conditions, what? If they stack, why are they not listed together in each other's ability descriptions?