I am looking to replace my Norton 4k in my progression. I currently go from a Naniwa 1k, to a Norton 4k, to a Norton 8k, to a Japanese Natural for finishing. Any votes on what would be the best replacement for the Norton 4k? I really hate the way the Norton 4k feels compared to the rest. I'd love to replace it with a Natural stone, but I can't find a clear replacement.