Shapton Professional Kuromaku 8000 Grit Sharpening Stone
Shapton Kuromaku Professional Whetstone, 8000 Grit, #K0710
210mm x 70mm, 15mm thick.
These Kuromaku/Professional series stones are very fast cutting and long-lasting, offering nice sharpening feedback while still being very hard so they resist dishing nicely. Note that these are splash-and-go, so do not soak these stones.
These stones come in a convenient plastic case that also doubles as a stone holder, though the affordable Naniwa universal/adjustable stone holder also works fine for these stones and will certainly be more stable and secure.