I'm going to wade in with an odd, ill-informed reply...

Having only ever used and had a Norton 4/8 and a Shapton 16k I find it hard to understand why one would want more than a 16k. As someone said, I don't know what I don't know, but with ten strokes (remedial fashion) on the 16k delivering what seems, to me, to be a pretty good shave ready edge, I'm not sure it's warranted...