Perhaps, if you were asking the question about original Gibbs and Jeffery rifles, it may be valid to compare feeding efficiency, but since they are very rare rifles, the average shooter is never going be forced to make a decision between the two!.

How other Gunmakers go about the business of achieving reliable feed, in these chamberings (or any other), is anybody's guess.

Ballistically they can be considered clones, so IMO, the only reason to diffentiate between the two is whether you want to build a 500 Jeffery on a standard length action, or use a magnum length action for the Gibbs round.

That, and the ease of 'smithing the single stack feed system for the Jeffery round.