I think this subject has come up before. In a past life I was very intimate with tooling - specifically stamping. Some of the tools had .0001-.0002" clearance between punch and die. Obviously alignment is critical and no mater how many times you draw tool steel or buy the best carbide, it's gonna move over time. If you cryo treat these pieces they remain very stable for a long, long time. In a tube the distances between parts vary millions times more in the manufacturing process than the stability a cryo treatment could possibly provide. My BS-o-Meter is coming to life....
In copper the conductivity of the product after annealing has nothing to do with grain structure (alignment, elongation, etc.) as this characteristic is independent of it. However, the oxygen further combining with impurities during the annealing process to cleanse (for lack of a better word) the PURE copper, does, because it binds with the impurities. Oxygen free copper is refined to remove ox and other impurities due to the detrimental effects of these in product applications. Pure Silver is at 106 IACS (conductivity), Pure copper (w/oxygen) is at 103, Oxygen free copper (the stuff we use) is at 101. IM very HO, cryo treatment to somehow improve electrical characteristics is total BS. I have been personally involved with testing conductivity of copper and many different alloys of copper - including: heat treating, pickling, and plating of those variations. Impurities (incumbent or added) or alloying copper affects conductivity, period.
I'd also be willing to bet that screen, grid, and plate materials vary WAY more in composition than any outside secondary "treatment" could possibly have an effect on. I would also wonder what effect cryo has on the glass? Surely the wires and glass have different dynamics at these temperatures? Soft vacuum possibly causing the "difference" in performance? Hmmm....
My BS-o-Meter is pegged...
Jim