I just noticed this topic.
And I can only share my experiences on this matter.
I also use DBF and CDX on network and on different kind of servers (Windows, Linux, NAS, ...).
It has been many years ago that I had any speed problem.
I remember the SMB2 problem on old Windows versions, but since Windows 7, I never experienced the problem again.
I have database which often are as big as 2 GB with sometimes more than 50 indexes in the CDX.
So, I get the impression that something must be wrong in the hardware is speed is a problem.
This happened to my twice, but meanwhile more than 10 years ago: a customer of mine was experiencing that my software was running very slowly. I spook about it with his PC-supplier.
Suddenly the supplier suggested to replace the motherboard of the PC, although all other software was running just fine. He replaced the motherboard and the problem was completely gone.
One year later, I had the same problem on the system of another customer. The same action solved the problem.
Just saying.