SFP28 would make zero difference at this point in time, your issue is something else, likely at the server side.
SerDes is 100% used, it's the heart of what gets data from the ASIC to the physical interface itself. SERDES is sometimes also called the PHY controller (or SERDES PHY). It's not used on the SFP module itself though. Right now we're at 112Gbps SERDES x 512 lanes to drive 64x 800Gbps interfaces on a single switch. I'm no EE expert though but this should help explain it better if you want to dive deeper:
https://docs.broadcom.com/doc/56980-DG
reverseslayer reacted to Lurick in SFP28 VS QSFP+
