Interesting journey David! I think you are, through trial and error, seeking a heat treat regime which is optimal in some sense for clean steel.
It is well-known that a key to forging tougher steel is to keep the grain size small (this is one of the important features of particle steel, CPM). About 20 years ago, a Prof. Verhoeven of Iowa State was (aside from his academic metallurgy) working with blacksmiths on various projects. He decided there needed to be a text which was not dumbed-down, but which could be read and used by educated non-metallurgists. The book is ‘Steel Metallurgy for the Non-Metallurgist’. It is expensive when you can find it. But because Prof. Verhoeven’s work was paid from public dollars, he made a copy of the book available to everyone on-line. And here it is:
You might find something that rings a bell in Chapter 8, ‘Control of Grain Size by Heat Treatment and Forging’. Two specific techniques, Phase Transformation and Recrystallization, are described starting p. 66 or so. Essentially they involve triggering new sets of grains to form, by heating and cooling, and by hammering. The point is, that each new set of grains is seeded inside the boundaries of the old grain set, and hence can be reduced to very fine size by repeated heating and cooling, with or without mashing down the cross-section by forging.