What is the best BNC Digital Cable under $4,000?

What is the application you’re using it for? To a DAC or as a clock? I use a mix of Transparent Ref XL and Marigo Apparition Extreme in both these uses. Either are excellent clock cables but as DAC cables the Ref XL is warmer and works very well with red book transmission, I favor the Marigo for direct DSD.

@mzkmxcv. While I know I’m beating my head against a wall let me try...

first you have to believe that superior clocking can improve the performance of a digital system. If, as is the case in my system or any other dCS rig, adding an off board clock (or in turn a 10MHz Reference to that clock) can improve soundstaging and definition then does it not follow that improving the accuracy of transmission of the clock signals in between the different components is also audible? 

The same logic holds for other non reclocked transmission paths such as AES/EBU and redbook over 75ohm as the OPs case. Reclocked standards such as USB behave differently and I have limited experience in this use case.

If on the other hand you believe that all digital connections are indistinguishable from one another and that CD=perfect Sound forever, then we are wasting our time and you can happily believe that none of this stuff matters and hoard your precious pennies for whatever else you want.

Soundstaging is actually all about definition, ie the relative accuracy of the timing of different sounds reaching the ears. Superior clocking improves the ability of the digital system to render all of the elements of the mix, including the reflected sounds in the mix, and hence recreate the original soundstage. The same holds for leading edges of sharp percussive sounds, or trailing decays, both of which are also aspects of definition.

The description above holds true for all system improvements, but it is something you’re likely to hear with improved clocking.

As to USB as I do not use this interface I have no opinion, I reserve my shared opinions for things I have actual experience of.