A few months ago, I bought 2 10GbE NICs off Ebay to connect my main desktop and basement server directly. Since then, I've never seen a transfer between them that was slower than 120 MB/s, usually about 160-200 MB/s. (no RAID or NVMe to NVMe transfers)

Some advice: make sure you know the form factor of your NICs. I accidentally bought FlexibleLOM cards. They look suspiciously like PCIe x8, but won't quite fit. FlexibleLOM to PCIe x8 adapters are cheap though.