FWIW I have a Norton 4k and love it. Great feel and cuts well for it's grit. Not as buttery as a Rika 5k, but still gives me that knife knerd satisfaction when using it. Sorry if off topic. I'm assuming you're talking about the Arkansas black 4k referred to in the chart. Just saw the Norton next to it and had to show it some love
Looks like they left a 0 off that first Sigma 1000x.
I've tried a couple Black Arkansas stones on knives and couldn't really tell (by sight or feel) that they were doing anything at all. It was kind of like trying to sharpen on marble.