I connected the K2002 (without preamp) to a nice Julie Research Labs NB-102 4 wire, oil filled, 100 ohm wire wound resistor. This resistor was probably over 30 years old. Setting the K2002 up in 4 wire, offset comp, 30 sample avg I had less than 100u ohm of measurement noise over 20 minutes. This would indicate 1 ppm measurement noise or short term stability.
I will check the K2001 later.