PM Utopian about your Carborundum barber hone. He collects them, so should be able to get you squared away on it.
Out of the 6 barber hones in my possession, none polish less than an 8K stone. Most are beyond that. But I don't personally own a carborundum, or a 103 so I can't comment on it specifically. If I remember right I was told it gives a shave about equivalent to a Swaty barber hone, which is pretty decent - around 8K give or take a bit. I have a razor in my rotation that gets maintained exclusively with a Swaty and linen/leather for what that's worth.