Great info in this thread! I usually finish on a '15k' natural stone, but was always curious as to the difference a 20k stone would make. Then I read my stropping (cotton/suede/cordovan) is the equivalent of an even higher grit!? So decided not to purchase it.
I always wince at honing stones posts, as I remember throwing a couple away when volunteering at Oxfam. I was only young but have never seen any hones like them. They sat in their own mahogany box, quite large probably a metre by half a metre, had the same colour as an angry rain cloud with a hint of blue and were shiny. Wonder what they were. I threw them in a skip, I'll never forgive myself.
Don't be too harsh on yourself, Nishy! I grew up in Sheffield in the 80's so imagine how many great razors I missed out on at car boot sales and the like when they weren't in fashion.