I have only missed a handful of shots due to not getting focus quick enough.
My opinion of Pentax screw drive is that it works pretty dang good and good enough for me.
Most of my lenses have quick shift so I can manually get into or close to focus and then let the camera/lens do its thing which is a plus.
To be honest, the quickest focus lens in my stable is the Sigma 18~300 and I believe the reason is that it has such a short focus throw.
A lot of photographers do not like the super zooms.
My Sigma is not the sharpest throughout its range but it can surprise you at times.
Very good walk a bout lens.
The brighter it is the better but even in lower light the pictures appeal to me and look like a film shot with some grain which I like.
My signature lists all my lenses.
I am not buying anymore, I am not buying anymore, I am not buying anymore.
Well, that is what I tell myself
Clarence