I have a pen sketch scanned with resolution ~ 7000x5000px 300DPI. When I'm trying to trace the whole image with Illustrator CS6 into b/w, I am losing details overall. Example is on the left side. It's just part of the image.
However, when I tried to isolate a couple small raster pictures from the big one and trace them separately, I got pretty good results comparing to tracing a whole picture. The isolated images are with resolution ~700x800px 300DPI. The problem is that I can't isolate all elements in sketch then combine after tracing, it's hell lot of work. So my hope is that there is some technique of tracing big images to get better quality.