i think, from experience on various "adventure" bikes, that the screens with a spoiler of some sort are the most effective at cleaning up the airflow.
I particularly like the "givi airflow" models which have a fairly large screen over the front of the main screen - the science is that the outerscreen creates a venturi effect which smooths the airflow and channels it over your head. They are very effective but they don't make a model for the LC GS for some reason. "fred" from this forum has actually made one using a 3rd party screen and spare givi airflow parts.
I bought the MRA spoiler with the clamps to try it on the std GSA screen and this worked very well - in the end I bought a 3rd party GSA-rep screen and drilled it to permanently mount the spoiler - it works fantastically well - I wear an open-face helmet for touring and it is comfortable at farily high speeds with no windblast and certainly no turbulence. I'l try and get a picture up later, but I certainly think its the way to go.