Russ,
Don't have an answer for you but do have dumb question.
From a "fastener use" viewpoint....... Why does it matter if the pitch is maintained or is gradual?
The stress point is moved and intensification factor would still be subjective, and in calc's, the max loading would still be based on the thread geometry.
Even the max loading is subjective.
Just wondering if you are needing to address someones spec for the bolt........
RICH