Recommendations for a good audiophile digital coax (BNC-BNC) 50 ohm cable?

Most wordclock connections I’ve seen specify a 75-ohm cable. I don’t know if that’s the case for your gear, but 50-ohm connections typically are used for circuits carrying considerable power. May be worth a check to make sure you get the right cable for the job.

I sincerely doubt you’ll have anything to complain about with a standard cable assembly made by Amphenol or other such vendor, but of course the boutique cable manufacturers do make a much nicer looking product.

Thanks, very helpful. The clock is Mutec Ref 10, and they recommend the 50 ohm connection with the Esoteric K1. I was also puzzled, perhaps should check directly with them.

Rajah, Short cables (<1ft) don't have to be impedance matched for average CDP to DAC connection, but your clock provides, according to description, "a very high slew rate", making it necessary to match impedance.  Also, this cable normally should be >1.5m, but because of this high slew rate 1m should be fine.  You can find 1m BNC-BNC 50ohm cables in Digi-Key or Amazon, like this one:

https://www.amazon.com/SDTC-Tech-Coaxial-Antenna-Connector/dp/B07Q3BJ8BV/ref=sr_1_3?keywords=50ohm+coaxial+bnc+cable+1m&qid=1577289259&sr=8-3

I am also a firm believer in Wireworld wire, use their BNC terminated cable between my Esoteric player and word clock.
You can also try cables from HAVE, Inc., they have standard ones as well will make up special cables for you with any ends that you may need. They use both Mogami and Canare wire products.

Oh, I see the Mutec has both 75-ohm and 50-ohm outputs; I’d guess the K1 has a 50-ohm circuit, so Mutec suggests you match it.

If you bought one of these Amphenol cables (almost free) you would at least have a baseline for assessing the boutique ones. Amphenol has been designing and selling radio-frequency cable and connectors for generations for commercial and military use. It’s hard to imagine that a specialist cable manufacturer working out of a small shop knows RF technology better. With such a cheap baseline, you can decide for yourself (you might want to ask Mutec their opinion -- they are sensible people).