The two best sets I've had on a Renix XJ was OEM and Morosso blue max straight boot spiral wound cables.
I imagine the Summit spiral wound cables, already cut and made at $27.50 are about the best price your gonna find.
I've tried about two dozen different kinds/sets of cables on various XJ's over the years. There are differences, not so much in performance, but at idle.
My 88 idles really nice, doesn't miss a beat. Sounds good with the sport exhaust and the steady beat, at idle.
Sorry the second link leads to search, I can't seem to paste the exact cable I have now.