As others have said, it is the perception of the individual riding the bike that matters. I generally use stems that are 60mm but have used 50mm stems as well and don't really notice so much difference that i cannot get used to it immediately. I asked a similar question some time ago
here. I also had a member in one of my other threads suggest a method for getting the proper reach adjustment that worked well for me. He said for me to put my elbow against the front tip of the seat and that with my fingers extended, the tip of my middle finger should reach the center of the bars. Some may find that to be short for their liking, but it was spot on for me. Might be something worth checking out.