Just my opinion, but I think the 577 NE doesn't penetrate at Nitro express velocities as well as the 500 NE which may not penetrate as well as 458 caliber bullets at faster than nitro express velocities.

The extra weight of the 577 Nitro Doubles seems a liabilty for the penetration expected.

A table for armchair hunters to chew on!!
http://www.grosswildjagd.de/penetr2.htm

I would think the 500 NE, Jeffery,505 Gibbs et al at around 2150-2400fps in an 11 pound gun have the optimum compromise of penetration, bullet frontal area, weight, and recoil in an Ele rifle at Nitro velocities.

But what do I know?? I have never hunted/shot Ele or any DG.
Someday I hope to resolve this issue.