http://aptirrelevance.com/otscreenshots/index.php has screenshots for comparison which include PAL & NTSC GOUT, but that is ANH only.
The gist of the other thread is that ROTJ is probably slightly improved in PAL vs NTSC, but not ANH and ESB. The reason is unclear.
Also be aware, the PAL DVDs seem to be cropped more (in ANH and ESB, just differently in ROTJ).
http://originaltrilogy.com/forum/topic.cfm/Are-the-PAL-GOUT-DVDs-upscaled-from-the-NTSC-masters/topic/6531/
http://originaltrilogy.com/forum/topic.cfm/GOUT-improved-versions/topic/11377/