I keep swapping to the London Reference I am comparing the Hyperion to, and it seems the higher the impedance loading, the closer they sound. I am not experiencing the "peaked high end" I was warned of if loading is increased over 1000Ω.
@dogberry It does not matter what the manufacturer suggests for loading of any LOMC cartridge, of which the SS Hyperion is an example (no matter what anyone says...).
Any brightness is usually not the fault of the cartridge so loading will not fix it. IOW If loading does fix the brightness, the cartridge wasn't the problem.
The phono section is.
This is because any LOMC cartridge generates RFI due to the cartridge's very low inductance, in parallel with the tonearm cable capacitance. That sets up an RF peak (usually 1-5MHz) which can oscillate, generating RFI up to 30dB higher than the cartridge signal level, injected directly into the phono section input!
If the phono section does not like that, it might distort, which will be interpreted by the ear as brightness. The loading resistor detunes that RF peak I mentioned, thus killing the RFI and the brightness. But the cartridge itself was unaffected. This is very easy to measure and demonstrate.
What this says is that when the manufacturer of the cartridge suggests a 'loading' value, then there's a good change the phono section he's using has this problem of RFI sensitivity; IOW its designer ignored the implications of putting an inductor in parallel with a capacitance (electronics 101, 1st week).
If on the other hand the phono section is immune to the RFI thus present at its input, its plug and play- no messing with 'loading' resistors- you'll find they have no effect.