Other ideas that occur to me:
Try switching off smooth polygons for the object, in case it is interfering with the bump on the curved parts of the geometry (where the artifacts are worst).
The bump map is very high contrast, which would produce some big normal shifts at the points of transition between white and dark grey. I would try reducing the contrast of that a little (using texture strength on the image node) or perhaps using a slightly blurred version of the map.
Also, I would try plugging it into Displacement instead of bump, to see if it does the same thing. I"ve found displacement produces more consistent results than bump for a tiling texture I've been working on.
You may well have been there, tried all that already.... :O)

"If I were a shadow, I know I wouldn't like to be half of what I should be."
Mr Otsuka, the old black tomcat in Kafka on the Shore (Haruki Murakami)