Dear friend: The ideal is that with the correct load impedance the frecuency response of the cartridge will be flat, but you need some tools and instrument to do that. So, if you are experienced in live music then you have to trust in you ears: take 3-4 records that are your standard and that you know extremly well and try differents impedance values till you are satisfied. Remember that the impedance ( in phono cartridges ) function like an equalizer. Be carefully.
Best regards.
Raul.
Best regards.
Raul.