I tried that 12k to Escher on a Charlie Lewis frameback last night. I did 50 laps on the blue/green Escher (weight of the blade) with water only. The 12k edge had been good on the shave test a week or so ago but last night's shaving edge was even better.
In terms of honing I don't think there are absolutes. As Glen was saying, what works for one guy might not work for another. Sham isn't wrong in saying that the Escher should be gone to at the 12k level but , like you, I've gone to my Escher after the 8k or the coticule many times with stellar results.
I know that Gary tried a couple of first rate Eschers and he personally didn't like the edges off of them. The Topher, my original honing mentor when he was around, didn't like his 8x3 natural coticule's edges and sold it to me. It is unreservedly the best coticule out of many that I have had. So it is really a personal preference thing. Many guys have posted in the past that they are perfectly happy with the shave they get from their 8k Norton. In addition to the YMMV nature of the results you also have the variations in the stones so it never ends. That is why I experiment and find what I like. I am open minded to what the other guy says but none of it is carved in stone. :)