Pioneer PL630- upgrading the phono cable?

an upgraded Audio Quest 404B (essentially a Hana Umami Red) Moving Coil cartridge.

What does this mean? Is it lower output / impedance now?

No- this is more of a purist's question regarding the ability for me to perceive an audible difference if I replace the 44 year old OEM cable with a higher end aftermarket phono cable that offers better RF insulation, lower capacitance, and SUPPOSEDLY a more transparent sound to the preamp. 

For clarity, I replaced my Shure V-15 Type IV moving magnet cartridge with a much better Audio Quest Moving Coil cartridge.

Having low phono cable capacitance is important with MM cartridges, but it's not likely to be an issue with MC, unless perhaps you're using some odd cable. As for RF, you may get better results by using a shielded cable, but on the other hand you may not - the only way to know is to try.

If it's a cable that was OEM to go with the Pioneer TT, chances are that you can easily do better without spending a lot of money.  On the other hand, there is no urgency.  Why not listen to the OEM cable for a few weeks, then purchase a reasonable cost modern alternative?  Do you live in an area with high RF pollution?  If not, shielding may not be necessary, and without shielding, capacitance can be lower than with.  That's if capacitance is of concern.