Done 24/0, 20/4 and 18/6 on my three...not a noticeable difference to me between 20/4 and 24/0. But I did notice that my 18/6 grow was fluffier and smaller. Of course, I was under CFLs for those. So I'm not good for giving info on HPS setups.
And attempt #2 is currently on its way. Let's see if you get ground powder again.