the center adjustment point on the cable acts more like a 'coarse' adjustment. get it in the ball park with that, then tune it at the lever.. thats been how mine is.
I agree with spock on the possibility of the clutch going 'over center', but I think you have have warped plates in the clutch itself.. that will cause all sorts of drag on the clutch.
just remember, you only create a very small gap in the clutch plates when you pull the lever.. maybe as small as a couple hundredths of an inch. it dont take a lot of warp in a plate to cause drag. also, glazing or other foreign material on the steel plates can cause the same.
my clutch, when cold, is a dream.. very little drag, other than what the oil in the clutch is causing. However, as it warms up, it becomes a total biatch to shift, up or down, (especially in the lower gears). If I ride until totally warmed up (like 30 miles, fully warm engine, oil, water), its still dragging, but its better. What I am figuring happens on mine, is that I have a couple plates with warping, or debris on them, and they are expanding at different rate in that area as the rest are, causing my problems.