Clearly, For us it is clear where the differences come from: shielding, shielding, shielding.
+1. Agreed. I use Supra CAT 8.1 as short endpoint cables between my FMC's + a double shield around the cable configured in a JSSG 360 loop does the trick. Some Techflex around it, and done. Ethernet 'radiation' is hampering the rest of your system. Also, (possible) leakage currents between the components can be a reason ethernet cables 'sounds' different. (despite ethernet is transformer coupled). That is why (galvanic/medical) ethernet filters work. Your system is performing better, as a whole, due to better shielding and breaking of detrimental currents between components.