When you say coticule, I assume you're referring to the yellow coticule rather than the belgian blue?

The yellow coticule will not replace the 4000 Norton in any way. It could replace the 8000 side, but is a much slower albeit far superior polisher than the 8000. I think the yellow is rated at somewhere between 10000-12000 grit.

Can you describe a bit more detail about what kind of problem you're having with getting your boker sharp? Is is sharp in certain parts along the edge and not others?

I think it would help if you gave a detail of describing the edge and how it felt when you shaved with it, and also describe your process to get it where you have it now.

No less or no more pressure on the coticule than the 8000 Norton. I love my yellow coticule. I think it's an unparalleled polishing stone. It's a finish stone as a final stage prior to stropping and isn't meant to be used for any work heavier than that. This means that the edge must be good and keen from the lesser grits prior to bringing it to the coticule. The coticule is like a master veteran world class performer. It assumes and even expects that you've got everything prepared for it before its performance. Then it goes out and wows you and the edge. If you don't prepare/prep the edge for the master coticule, it will walk offstage and just get back into the limo.