I have an odd observation and I'd be interested if others have the same, or it's just a bunch of coincidences. Whilst juggling my PCIe cards around to find room for the Arctic Tern board I moved my graphics card (a WX9100) from CPU 2 to CPU 1, and suddenly the machine feels snappier.
I'm running Debian 11 and CPU 1 appears to be doing most of the work (judging by which runs the hottest) so I'm wondering if that's what makes the difference. I always had the impression the graphics were laggy, but now all of a sudden the system feels a lot more usable. That said, the OS received updates, the internal VGA is now disabled, probably other stuff, and the PSU was replaced (the logs were full of MasterDetectionFailure and I got it down to a PSU fault).