I am using a Mercury 3 in my system for a larger project. I have been testing with Ropiee (UPnP) and PiCore Player. The Mercury 3 has a Pi4 as the core computing hardware rather than a CM4. I am booting PCP from a fast 256GB USB, and I have a 4TB SSD for music. I have not perceived any performance issues running LMS and Squeezelite on the new Mercury 3.
When running Ropieee, I use my SGC Sonic Transporter I5 for Minimserver or Roon. I have also been testing the new Linux version of Audirvana on the server.