I use 12W @ 10cm/s with the wet paper technique, it usually produces excellent results. The scan gap setting should be 0.1 (254dpi) or 0.2 (127dpi) depending on the image (lower resolution in glass often produces a better final image at higher power, or the higher resolution if you are using a very light engraving).
Before you dither the photo in Photoshop, first scale it to the correct size. So if you want a 4"x3" design (at 127dpi), 508 pixels x 381 pixels. Then I always enhance the contrast and convert to greyscale before applying the dither filter (the filter I have allows you to preview the results and change parameters to get the look you want - not sure if you have that capability). Once dithered save it and import to Newlydraw, do not change the size or you mess up the process. Engrave at the same resolution you originally used.
I'm not sure if I have any examples in the shop that I can provide - but I will have a look.