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Comparing absolute grit size is difficult regarding the results you get. The grit shap is important too.
Coticule grit is typically 8000 grit in size, but due to its shape, it cuts like you'd expect...

I think it should work. Maybe it's not ideal, but ultimately, there is little difference between
8K->12K
6K->12K

If a razor needs more honing, the 6K will be somewhat slower than 4K, but I see...