Jason,
Have you thought at all about the 358 JDJ cartridge?
If you do not know its built on a 444 Marlin case. This case is basically a rimmed '06 case. Just a bit short.

This pic shows L/R 35 Rem, 358 Win, 358 JDJ, 35 Whelen, 9x57, 375 JDJ and a 9.3 x57.
It's ballistics are mostly out of short (long) pistol barrels say 14". But from a 20-24" barrel another couple hundred FPS would be added.
In my mind some of the biggest hurtles with wild cats like the Greevy is the cost of dies. ( And reamers and nusance of foarming brass) I know you have a place with DOC that covers this. But the JDJ has both fact head stamped brass and dies avalible.
I had a Contender barrel so chambered. I traded it off pretty quickly do not remember the situation. I do remember loading these for the buddie who got it from me. I was hot for my 357 Herrett at the time.

If nothing else, food for thought.