Dicebot:
I did explore issue a bit and reported results in a blog post (snippets are really small and simple) : http://dicebot.blogspot.com/2013/05/short-performance-tuning-story.html
In the first of his posts I don't see -noboundscheck used, and it compares different algorithms from C++ (a switch) and D (two nested ifs, that are not optimal).
From my experience if you have some care you are able to write D code for LDC that is about as fast as equivalent as C code, or better.
One open question remains though - can D/Phobos do better here?
Of course. Bye, bearophile
