Question for Audio Research Ref 5 owners ?

What power cord have you found that works best with this line stage.Have several 15 amps and only one 20 amp.Using it on the Ref 110.Just curious as to what you might think and thanks for your time.
I've used a Nordost Valhalla and a Silent Source Signature PC with excellent results and the difference was not vast but, I've heard ARC uses Shunyata. As with all things audio what works in my system may not work as well in yours.
I have used Shunyata Python Helix alpha with the REF5, but upgraded to Anaconda Helix alpha for the the Anniversary REF40.