Longtime lurker, first time poster here!
I have a 2010 cMP 12-core 3.33, 96GB in which I've run a 10GbE SolarFlare SFN5122F PCIe (with fiber SFP+) from HiSierra through Catalina. I had also used an Aquantia AQN107 10Gbase-T PCIe card that was plug-n-play up through Catalina.
Then, things soured in Big Sur, when the Aquantia card was deprecated by Apple. I used a flashed Alpine Ridge Thunderbolt card in slot-4 and tried the QNAP QNA=T310G1S and the Sonnet Solo10G SFP+. I had returned the QNAP because I was disappointed in the performance (~5Gbps) compared to how well the SolarFlare card worked (~8Gbps). After trying the Sonnet product (~6Gbps) I returned it because it didn't seem like much of a value, and certainly physically felt hotter than the QNAP. [My laser thermometer was lost at the time, so I don't have numbers. I have since found it.]. The Sonnet got returned too.
I briefly tested the 10GbE connection of the AKiTio Thunder3 Dock Pro in the M1 Max Studio that I had for about a month, and it seemed to offer ~7Gbps performance in informal testing. [The M1 Max Studio got returned because (long story) it would not properly wake from sleep, probably because of the Sabrent external boot drive. Yay, Costco!] Back to Ethernet issues I am awaiting another flashed Alpine Ridge card, and will use the AKiTio Dock w/10GbE until the Apple M2 product line has something I want.
Take note, that when using the 2010 cMP as an SMB server, its performance never gets better than about 200MByte/s (<2Gbps) even directly presenting a shared NVMe drive on the network, whereas, as an SMB client, it'll do ~8Gbps. I'm not sure why. Because of that, and power consumption, I use old HP Z220 convertible mini-towers running Win10 Pro as the "servers" on the network. They all have the SolarFlare SFN5122F cards and are quite stable. Two of them have motherboard RAID, and the third has SAS drives with an Areca RAID controller.
Whew! Hope that helps.