A limit of right speech
From Abhaya sutta:


  [1] In the case of words that the Tathagata knows to be unfactual,
  untrue, unbeneficial (or: not connected with the goal), unendearing &amp;
  disagreeable to others, he does not say them.
  
  [2] In the case of words that the Tathagata knows to be factual, true,
  unbeneficial, unendearing &amp; disagreeable to others, he does not say
  them.
  
  [3] In the case of words that the Tathagata knows to be factual, true,
  beneficial, but unendearing &amp; disagreeable to others, he has a sense
  of the proper time for saying them.
  
  [4] In the case of words that the Tathagata knows to be unfactual,
  untrue, unbeneficial, but endearing &amp; agreeable to others, he does not
  say them.
  
  [5] In the case of words that the Tathagata knows to be factual, true,
  unbeneficial, but endearing &amp; agreeable to others, he does not say
  them.
  
  [6] In the case of words that the Tathagata knows to be factual, true,
  beneficial, and endearing &amp; agreeable to others, he has a sense of the
  proper time for saying them. Why is that? Because the Tathagata has
  sympathy for living beings."


https://www.accesstoinsight.org/tipitaka/mn/mn.058.than.html

This sutta is also interesting, because it suggests that being silent can sometimes be wrong speech in a sense. There may be situations where we need to speak up to prevent harm. Right speech then becomes a question of knowing when to remain silent and when to speak up. Timing becomes a factor.

What is considered factual, true, beneficial, endearing &amp; agreeable, and not least proper timing will probably always be subjective to a certain degree, so it's hard to draw a clean cut line between right/wrong speech. One will always need be mindful to make good judgements, i suppose.