Fastest but still reliable way to check if in a comment

The conventional way to check if we are in a comment would be to
evaluate 

  (nth 4 (syntax-ppss))

and see if the result is non-nil.  The computation is not cheap, which
is an issue if we are using this function in a loop.  Does anyone have
another idea what to do in that case?  My best guess would be to check
the face at point:

  (memq (get-text-property (point) 'face)
                            '(font-lock-comment-delimiter-face
                              font-lock-comment-face))