Success: Mac Studio 25GbE
I have always been frustrated at the 10Gb Ethernet in the Mac Studio. It could easily run much faster networking using Thunderbolt. This would make it a lot easier to work with networked storage rather than Direct Attached Storage over Thunderbolt like my OWC Thunderbay 8. My ultimate goal was to set up the highest possible speed networking between my Mac Studio and my NAS (a Dell R640 with dual SFP28 networking).
There are several Thunderbolt to 25GbE adapters, they cost $1000 and up. There had to be a cheaper way to do this. I found it.
I got a Sonnettech SE I T5 and installed a ConnectX 4LX card in it. I got the card on eBay for about $25. It has two SFP28 ports on the card, which I connected to a UniFi Pro Aggregation Switch using copper DAC cables. Now I am getting iperf3 tests around 20Gbps. I can do better.
The Pro Agg switch has four SFP28 ports and a LOT of SFP+ 10GbE ports. I have both ports of the Mac ConnectX card plugged into the switch. Now I could use LACP to aggregate two SFP28 ports for even higher speeds. I'm not sure it will increase performance, I think MacOS supports SMB multichannel. I have some tuning to do just on the single SFP28 connection before I set up LACP.