My son was bored last night, so decided to do a bit of skip diving.
Result. An older PC with a 6 core 12 thread 3960X processor on a workstation class motherboard (X79), with 8 memory slots populated with 16GB of memory and an Nvidia GTX 970 GPU. In a decent case able to hold 9 hard disks.
Best thing is it all works, My server has been upgraded now populated with 40GB memory, And can now stream 4K video from Plex without buffering.
And my son will have a bit of extra pocket money selling the GTX in these times if GPU shortages. The whole thing scored 10,500 in Firestrike benchmark.
A high-end motherboard can certainly improve disk and network performance, as on paper it should have only been a minor upgrade (original server had an i7 4770S