Zero evidence any specific weight is more/less accurate/consistent.
It's hard to have "evidence" for something that is only seen by the person playing. However, many top players are using pretty heavy and long cues, and several of them told me because it holds the line of the shot better. If you think about it purely in theory, the heavier the cue the less likely it is to be thrown off course, same as any other heavier thing. More mass, more effort to move it from the line it's already traveling.