Fewer turns with heavier-than-average wire is an option too, like the Lollar El Rayo humbucker.
Don't know what gauge Jason uses but they give pretty robust output from only 4K fbridge and 3.75K neck.
As for cryo treatment of silver winding wire, I suspect that could be more about mechanical properties than tone.
Silver has lower tensile strength than copper, so winding thin silver wire under any tension might be troublesome.
