I would START evaluating every cartridge at 47K if this is possible (or without supplementary loading resistors with a step-up transformer), and work my way down in binary increments (halving the load with each successive step).
You may well find some LOMC cartridges are fine at 47K.
I would NEVER advocate a universal loading rule however (as Raul states). If this was truly what HP recommended, it is misguided thinking.
Note that loading is contextual to not only the cartridge (rolling off ultrasonics), but to your phono stage (how it reacts to ultrasonics by ringing and misbehaving in other ways). There's a recent thread where Ralph (Atma-sphere) comments on this.
As usual, the correct answer is: "it depends".
Case in point: I've loaded my XV-1s with good results, anywhere from 35 ohms, to 47K - depending on the RIAA stage in use.
On my Atma-sphere MP-1, 47K is fine.
Treat loading the way you would tracking force and anti-skate. Apply just enough, and not too much. Too much of any of these parameters squashes dynamics, and too little is edgy (a necessary generalization to keep this post brief).
If the numbers tell you one thing, and your ears tell you another, guess which "instrument" you should trust.
Cheers,
Thom @ Galibier