... there was too much variability between maximum book loads...
Yes, this is always true. The test equipment, plus differences in primers, bullet construction, powder lots, etc. all have an effect. In the Hodgdon data, one could at least get the same bullet in a few of the .308 / .30-06 comparisons. Being unable to control all the variables makes it difficult to extrapolate or interpolate from load book data.
For what it's worth, I seldom go much beyond the starting loads in the books, and I keep my measured speeds to those levels.
