Yeah, these really are glacially slow - slowest cactus species there is.
So far these have been hard grown, without fertilizer, which could account for some of their smallness, well that and forgetting that I had them at the back of a table for a couple of years.
Grafting and the application of ferts are very tempting, but ferts can distort the form shape and if the roots are lopped off in favor of a grafting stock, these plants will never be on their roots again, as they are practically impossible to root again.
So, probably will just continue to be patient will these...for now.
dvg