Dan,
If you load 2mh inductance and reasonable capacitance figures (say 125pf) into a calculator for such things (
http://www.hagtech.com/loading.html) the real resonant point likely comes so far out of the audio band that it's probably inconsequential (which is why Grado notes 47K as the loading point).
Unfortunately with moving coils, the resonant point seems to occur at much lower values (for whatever reason) in the audio band, so low loading rates are needed. The peaks need to be squashed with most (maybe, all) moving coils.
On the higher output Prestige series, which plugged into the same calculator came out to 10-12K or so loading, it sounds best at 47K, too. I tried 11K and 32K, I thought 32K was improvement in some areas, but ultimately 47K sounded best for it

These calcs are all just a starting point...they don't take into account tip resonance and other matters. So, you end up using your ears in the end anyhow in the end

John
