> I also measured the primary Z using a B&K 879B LCR meter. With all secondaries open, it measures 4.35K at 1KHz
Coincidence. I wouldn't believe that measurement anyway. It should be a much larger positive or negative reactance (inductive if below resonance, capacitive if above. As far as 4.4K vs 5K vs 5.6K, 10% won't make much difference.