I have not read thru the mailing list posts so see what other comments there may be about this, but the posted system requirements,

https://surfer.nmr.mgh.harvard.edu/fswiki/SystemRequirements

- do not mention anything like Xeon class server chips.

Desktop (non-server class) machines with a modern Intel i7 or i9 chip with base (non-turbo, non-overclocked) CPU speeds of ~3 GHz are common.  I’ve run a complete recon-all in about 7-8 hours on a mid-2016 MacBook Pro with a 2.9Ghz  i7 chip (4 physical, 8 virtual cores) with 16GB of old higher latency DDR3 memory using all SSD disk storage (with the machine doing nothing else).

I don’t have any data w.r.t the pros/cons of L2 or L3 level cache.  I don’t know the details of how many threads the commands executed by recon-all can exploit.  From my own experience of running various commands, 4 or 8 physical cores (hyperthreaded to yield 8 or 16 cores) should be fine.   I’ve also found that 24G to 32G of RAM is helpful with performance.  Since data/files will be read/written from disk, at certain points performance could be I/O bound by how fast disk read/writes occur.  This can be helped by having your data stored on a 7200, 10,000 RPM disk drive (or better an SSD drive) to speed things up that is physically separate from the drive with the boot partition.

But you could certainly meet or upgrade the specs to outfit a server machine with Xeon class chips and drives for multiple users.

- R.