If you want a great 8K stone get a Suehiro G8 stone,it's a silicon carbide stone and it finish's like an aluminum oxide stone most people that have tried it seem to think it's the best in that grit range.
I own 2 of them in edge pro format and all I can say it is one of the best finishing stones out there and I can't praise it enough,just ask
HeavyHanded
he another one that loves the G8.
You can find them on ebay being sold from Japan for a very reasonable price,also if you have never tried any stones from Suehiro you don't what your missing out on every stone they make is of a very high quality and it's almost never you hear anyone complain about their stones.