Nice work, @buyproduct !
The only detail that jumped out at me was this:
Since we can’t ensure which donor PCB people are using, we can’t claim a 3-6ms constant. They could be using a very laggy donor PCB well beyond that range. I just wouldn’t want to give anyone the false security that their chain is faster than it actually is. And as I mentioned briefly earlier, in the case of non-USB donor PCBs, the constant would likely be well faster than for USB donors.