Two things worth mentioning, one is that the tail is indeed a net downforce (In a straight and level situation), Backpackers point is dead right, an aft c of g means the tail needs todo less work, less induced drag giving better fuel consumption. The other thing to say, more generally, is to not think about elevator deflection, but relative wind, as that is the true cause of lift, or otherwise, and what is actually happening. The static angle of incidence is only of note if the relative wind is from dead ahead.
The stability point doesnt really relate to downforce, it would be true if it were an upforce too, the stability explanation is more about moments produced by the tail to oppose the disturbance, and where the planes c of g is relative to the tail. An aft c og g means the tail is less effective stability wise as the distance betewwen te tailforce and pivot (cofg) is reduced, so the restorative moment is smaller