If anything is underrated, it's 6.5x55 Swede
Having shot 6.5mm Arisaka and a 8x57 Mauser for some time, I would have to say that I've been really, really tempted to pick up a rifle in 6.5x55 for no other reason than it seems like a great middle ground (not compromise). I'm not sure how 257 roberts stacks up against 6.5 swede, but that seems to be in the same BC/powder capacity arena. 260 Rem would be at the same family reunion in my gun cabinet.
7x57 is similar/dis-similar enough that it's remained on my long-list of "will gets."