Input the resistance and inductance for your cart, and input capacitance values to see what the resonant frequency is. I think anything above 20 KHz is fine, so capacitance values up to that resonant frequency should be OK.
Yikes! When you are dealing with LOMCs, there is no need to add any capacitance for loading! That has entirely to do with high output *moving Magnet* cartridges, where loading the cartridge does have an effect at audio frequencies.
By adding capacitance to a LOMC, you move the RF (Radio Frequency) resonant frequency *down*, but not likely into the audio band. The inductance of such cartridges is tiny, so the RF resonant frequency is going to be high. In any event, you will have to kill that resonance with a resistor, not a cap. IOW by adding capacitance in effect you have created a bit of a moving target.
Raul is correct, any amount of loading capacitance offered by the phono section is inconsequential at audio frequencies. It can have a huge affect at RF frequencies though; its the ability of your preamp to handle RFI (Radio Frequency Interference) that says how audible the loading is: the more RFI bothers your preamp, the more important you will find the loading.