I recently added a 2k because I felt I was spending too much time on the 4k. There hasnt been a dramatic difference, but I'm satisfied with it there. My 1k is a naniwa, so I got a 2k shapton to go with the rest of the progression. I was also thinking that 1k to 2k to 4k would be more in keeping with the idea of doubling the grits.

I have had problems integrating it. I know what tests I want passed on the 1k, 4k and 8k, but I have no tests for the 2k, so I just give it x number of laps, depending on the razor. Also, I actually overhoned a razor or two b/c of it.

I'm pretty sure I've read there are benefits to using a single progression of the same type of stones with really small jumps, but I cant vouch for this.