I haven't seen much information on either of these two lenses to the level that people get into testing a lot of stuff. I remember anecdotal information that the 40 has less barrel distortion than the 35, and read another review that the 40 lacked contrast vs the 35. Then again sample variation is supposedly pretty big with CV lenses. I've been lucky and not experienced anything that I would qualify as a poor copy but that might have been the case with the contrast difference claims.
Show me your film leaders and I will tell you what you are.