I've found setting mouse sensitivity to about 90% or around there, and turning on mouse smoothing helps play. At least for me.
Your shots look good Legend and I was suggesting you were lying in anyway. Rather that most people that post FPS shots above 40 @ 1680x are not taking shots of dense foliage with depth of field. Usually it's shallow depth of field or near water, not in dense underbrush.
I played the demo through @ 1680x all high save shader, textures and water very high and found performance acceptable. Yes I did go below 30FPS in fight scenes at times.
I'll go do a few suicide runs and post a action shot or two
As Xion suggests, I will also try reducing only
shaders and see how it impacts performance. I am curious and haven't tried that yet.