The answer to this question should be based on science, not opinion, but that's just my opinion.
How did you pick 6.7"? Why not 6.73", or 4", or 4.0173"?
Choosing 6.7" implies that you already know the correct answer to within one part in 67. That's better than 2%.
Is your post a flattery-based sales pitch disguised as a question?