Owners of Jelco arms?

Different systems, different ears and subjective listening preferences perhaps. Funny, but I found the high frequencies to quite possibly be the one area in which the Audio Sensibility Impact cable most showed its superiority to the Jelco cable (sounding much more natural, almost like a layer of grit had been removed) but it was pretty noticeable pretty much from top to bottom. No loss of transparency or spatial cues here. Just more music.

I'd be inclined to agree with a review of the AS cable posted below; that reviewer
essentially heard what I heard in terms of the AS vs. the Jelco. And the Jelco I was using had also been cryoed and burned in on an Audiodharma cable cooker and had been improved over the stock Jelco cable IMO. 

So yes, probably a good idea for the OP try try both cables from Steve. 

https://wallofsound.ca/audioreviews/a-truly-outstanding-120-phono-cable/

I’d like to upgrade my cable from the Jelco cable, considering a Synergistic Research Foundation cable. Anyone familiar with them?  For Jelco Tk-850l. 

I'm using the Jelco JAC 501 cable with my TK-850L MKII tonearm. These cables are sturdy and well made, uses high quality parts, and very neutral sounding in the few months I've had them. Unless you're wanting more highs or lacking something in your system and intend to use cables as a tone control, I don't see the point of spending more.

You might want to try NERVE Audio, I have 2 Jelco TK-850M tonearms and on both of them I use the Axon 24 Tonearm Cable, one with the 90 degree din plug and the other with the straight plug. Axon 24 Tonearm Cable – Nerve Audio On the one with the straight plug he even custom made it for me with a Zavfino 1877 TAD-3 Tonearm Connector.These are great cables that really bring out all the nuances on your vinyl. Just send Curtis an email and he will be happy to help you..