Different Bias currents? The more expensive one would be expected to have lower bias currents I would think = lower voltage drop (ideal diodes have a constant volage drop with current, real diodes don't) Also, it sounds like you were measuring one DMM with another DMM? You can't really do that since the DMM needs to have a much higher input impedance than the circuit impedances in order to have minimal impact on the circuit. Two DMMs- both very high, probably comparable input impedances = a lot of inaccuracy.