I bought a Bluetooth (+WiFi) PCIe card that is version 5.1 (hciconfig confirms).
My headset claims, in product description, also to be 5.x.
However, I'm unconvinced, or at least I don't think it's actually operating taking advantage of a newer protocol: I switched from v2.1, but blueman still reports ~16.6KB/s up and down in HSP/HFP (headset) mode, and ~41KB/s up, 370B/s down in A2DP mode.
Range does seem improved, but that could just be the more proper antenna it has now, vs. the tiny PCB-inside-USB-port thing I was using before; the rates mentioned are from sitting right next to it. Theoretically I should expect more like 125KB/s each way in headset & 250KB/s A2DP mode I believe.
How can I determine the protocol actually in use, or which my headset is detected as supporting? I had a brief look at its GATT characteristics, but it didn't seem to be there.