I have never used the .257 Roberts but if it performs anything like the 25/06 , it is a keeper.
I went through a period in the 80's that I put my 25/06 to regular use and killed bull elk and moose with it and it worked well with Nosler Partitions.
If the .257 Roberts works like a slightly reduced 25/06 it would make a hunter quite happy.
I carried the model 700 around alot then and on many sheep hunts, my only issue was the barrel length....24" is just to long in a repeater.
Decades later, after trying most everything out there, I am back to the 30/06 and it's get.
Medium cartridge length, tapering shoulder, long necked rounds fit the bill.
Just need to see past all the marketing hype , the smoke and mirrors that the industry put out there.
Cheers