Well, I went ahead and bit the bullet with a J-nat. I decided to go bold and grab a Nakayama Asagi Koppa Lv. 5 vs. the Shoubudani type 100. I picked up a few Nagura as well so I could get my free shipping. Either way the price was gonna be the same why not get a few extra rocks right? Seems the only other Nagura I may need would be a Botan. I can't wait to try this out and see if I can get a working edge from it. I payed a little extra for real estate, but I figure a stone that heavily relies on slurry; that extra space is worth every penny. Here is a pic of the stone I grabbed;

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The max dimensions are: 210mm x 75mm... I would guess based on the width loss that is about a third, so about 50mm at the narrow end.