In simplest terms, input capacitance that is significantly higher than recommended creates a resonant peak that can creep into the audible range in the treble. Take a look at the first graph at the following link (
http://www.hagtech.com/loading.html) - it shows how the resonant peak becomes more audible as the pF loading is increased. Don't worry - you don't need to understand any of the math to understand the graph.
50 pF is quite low, so the ZP3 shouldn't cause any issues regardless of the MM cartridge that you are using. Many MM phono stages use 100 pF as the default. The cabling that you use contributes additional loading, so the total of the phono stage and the cabling input capacitance should be within the recommended range for the specific cartridge that you are using.
MC cartridges are typically not sensitive to input capacitance. Rather, they are sensitive to the input impedance, and the recommended values are in the general range of 100-1000 ohms. For nearly all MM carts, the recommended input impedance is a standard 47K ohms.
Hope this helps, Scott