Buscis2, the paragraph that you quoted is incorrect regarding a low impedance cartridge like the Helikon SL, since the low source impedance of the SL means that the frequency response within the audible band will not be altered by loading values.
With low-impedance cartridges and within the audible band, the frequency response of the cartridge itself is insensitive to what value you load it at (ambient temperature has a much bigger effect on the frequency response than the loading value).
Changing the loading _can_ create variations in the frequency response at the input of the phono stage, but these will be a result of how the source impedance and inductance of the cartridge interact with the interconnect cable's capacitance (which will therefore be affected by the length as well as the structure of the cable). Since the source impedance and inductance will be quite small with a low-impedance cartridge, these frequency variations will be at frequencies in excess of 500kHz, a wee bit higher than anything that you can hear directly.
Therefore with low-impedance cartridges, loading is mainly about giving the phono stage something that it can be happy with. Not the cartridge. For a manufacturer of low-impedance cartridges, it therefore doesn't make sense to provide a precise recommended figure for loading (apart from when stepup transformers are used), since the choice of interconnect cable (including length) and what the phono stage can tolerate will have a significant influence on what is perceived to be the optimal loading value.
As a general rule of thumb, the less linear the phono stage is at RF frequencies (the regions where loading will alter the frequency response), the heavier the loading will need to be to achieve listening satisfaction.
hth and regards, jonathan carr