The difference I see in the .257 Weatherby is in wind drift and trajectory, which makes it easier to hit with at longer ranges, even when using a multi-point reticle or twisting turrets. But also admit that one of the moderate 6.5s (anything from the 6.5x55/.260 class to the 6.5-06/PRC) works noticeably just as well in wind, and with laser rangefinders a flatter trajectory isn't a big deal either.
As I've noted in other posts, the longer I hunt big game, the less difference I see in "killing power" in almost any vaguely appropriate cartridge. This is contrary to what many believe about bullet diameter and weight, but as long as the bullet penetrates and expands sufficiently there doesn't seem to be much difference.
When I started using the .257 Roberts 35+ years ago I'd been using the .243 Winchester for around a decade. Just about everybody back then (especially the handloading rifle loonies) believed the .257 was superior to the .243 for deer, because of the heavier bullets available. But after using the .257 for a while I couldn't see any difference.
Now, I did step up to the .30-06 last fall when hunting in a favorite local area, but that's because grizzlies are becoming more common there. A few years ago my wife killed a cow elk in a similar, nearby area late in the evening, using her New Ultra Light Arms .257 Roberts--which also happened to be the only rifle we had along, though I did also carry a handgun and bear spray. I'll admit that returning to the elk during the pack-out process brought about thoughts about how effective a .257 Roberts with 100-grain Barnes TTSXs might (or might not) be on a grizzly--partly due to having some encounters with them over the years. But we managed to get the elk to the pickup without incident.
“Montana seems to me to be what a small boy would think Texas is like from hearing Texans.” John Steinbeck
