While LR stereo comps aren't ideal in that they don't replicate the soundstage and environment of our field recording, they -are- controlled. And since they're controlled, they will highlight the audible differences in the cables and the cables alone - if imperfectly relative to true field use - so that one may at least begin to identify the audible differences. In the current case, and the case of a LR comp, more listening is due - no question. But at least in the case of a LR comp we've introduced control to the initial comparison.
FWIW, there's an easy way to do a reasonably controlled comp: find someone with a stock R-4, or with the same Busman or Oade mod on both pairs of channels, run a single pair of mics, split the mic cables, set levels properly, and...voila! There's your comp. This is not hard to do. It is sometimes difficult arranging the appropriate gear and motivation from a taper willing to give it a go.
My R-4 is differently modded on both pairs of channels, unfortunately, else I'd offer to do it. If anyone wants to loan me a stock R-4 (or Busman R-4 with the same mod across all channels), I'll not only do the cable comp, I'll also comp stock/Busman v. Oade Warm and Transparent mods.