HSM vs SDM vs Screw Drive
Interesting question. My experience is my screw drive lenses have the same focus accuracy as my motor drive lenses. (Sony SAM and SAM II vs screw drive and Pentax SDM versus screw drive)
For a few Pentax lenses, some people have had intermittent problems with SDM drive and have had them converted to screw drive (by firmware) and have reported good results.